JCO Precision Oncology Conversations

JCO PO author Dr. Foldi at UPMC Hillman Cancer Center and University of Pittsburgh School of Medicine shares insights into the JCO PO article, "Personalized Circulating Tumor DNA Testing for Detection of Progression and Treatment Response Monitoring in Patients With Metastatic Invasive Lobular Carcinoma of the Breast." Host Dr. Rafeh Naqash and Dr. Foldi discuss how serial ctDNA testing in patients with mILC is feasible and may enable personalized surveillance and real-time therapeutic monitoring.
TRANSCRIPT
Dr. Rafeh Naqash: Hello, and welcome to JCO Precision Oncology Conversations, where we bring you engaging conversations with authors of clinically relevant and highly significant JCO PO articles. I am your host, Dr. Rafeh Naqash, podcast editor for JCO Precision Oncology and Associate Professor at the OU Health Stephenson Cancer Center at the University of Oklahoma.
Today, we are thrilled to be joined by Dr. Julia Foldi, Assistant Professor of Medicine in the Division of Hematology-Oncology at University of Pittsburgh School of Medicine and the Magee-Womens Hospital of the UPMC. She is also the lead and corresponding author of the JCO Precision Oncology article entitled "Personalized Circulating Tumor DNA Testing for Detection of Progression and Treatment Response Monitoring in Patients with Metastatic Invasive Lobular Carcinoma of the Breast."
At the time of this recording, our guest's disclosures will be linked in the transcript.
Julia, welcome to our podcast, and thank you for joining us today.
Dr. Julia Foldi: Thank you so much for having me. It is a pleasure.
Dr. Rafeh Naqash: Again, your manuscript and project address a few interesting things, so we will start with the basics, since we have a broad audience that comprises trainees, community oncologists, and obviously precision medicine experts as well.
So, let us start with invasive lobular breast carcinoma. I have been out of fellowship for several years now, and I do not know much about invasive lobular carcinoma. Could you tell us what it is, what some of the genomic characteristics are, why it is different, and why it is important to have a different way to understand disease biology and track disease status with this type of breast cancer?
Dr. Julia Foldi: Yes, thank you for that question. It is really important to frame this study. So, lobular breast cancers, which we shorten to ILC, are the second most common histologic subtype of breast cancer after ductal breast cancers. ILC makes up about 10 to 15 percent of all breast cancers, so it is relatively rare, but in the big scheme of things, because breast cancer is so common, this represents actually over 40,000 new diagnoses a year in the US of lobular breast cancers. What is unique about ILC is it is characterized by loss of an adhesion molecule, E-cadherin. It is encoded by the CDH1 gene. What it does is these tumors tend to form discohesive, single-file patterns and infiltrate into the tumor stroma, as opposed to ductal cancers, which generally form more cohesive masses. As we generally explain to patients, ductal cancers tend to form lumps, while lobular cancers often are not palpable because they infiltrate into the stroma.
This creates several challenges, particularly when it comes to imaging. In the diagnostic setting, we know that mammograms and ultrasounds have less sensitivity to detect lobular versus ductal breast cancer. When it comes to the metastatic setting, conventional imaging techniques like CT scans have less sensitivity to detect lobular lesions often. One other unique characteristic of ILC is that these tumors tend to have lower proliferation rates. Because our glucose-based PET scans depend on glucose uptake of proliferating cells, often these tumors also are not avid on conventional FDG-PET scans. It is a challenge for us to monitor these patients as they go through treatment. If you think about the metastatic setting, we start a new treatment, we image people every three to four cycles, about every three months, and we combine the imaging results with clinical assessment and tumor markers to decide if the treatment is working. But if your imaging is not reliable, sometimes even at diagnosis, to really detect these tumors, then really, how are we following these patients?
This is really the unique challenge in the metastatic setting in patients with lobular breast cancer: we cannot rely on the imaging to tell if patients are responding to treatment. This is where liquid biopsies are really, really important, and as the field is growing up and we have better and better technologies, lobular breast cancer is going to be a field where they are going to play an important role.
Dr. Rafeh Naqash: Thank you for that easy-to-understand background. The second aspect that I would like to have some context on, to help the audience understand why you did what you did, is ctDNA, tumor informed and non-informed. Could you tell us what these subtypes of liquid biopsies are and why you chose a tumor informed assay for your study?
Dr. Julia Foldi: Yes, it is really important to understand these differences. As you mentioned, there are two main platforms for liquid biopsy assays, circulating tumor DNA assays. I think what is more commonly used in the metastatic setting are non-tumor informed assays, or agnostic assays. These are generally next-generation sequencing-based assays that a lot of companies offer, like Guardant, Tempus, Caris, and FoundationOne. These do not require tumor tissue; they just require a blood sample, a plasma sample, essentially. The next-generation sequencing is done on cell-free DNA that is extracted from the plasma, and it is looking for any cell-free DNA and essentially, figuring out what part of the cell-free DNA comes from the tumor is done through a bioinformatics approach. Most of these assays are panel tests for cancer-associated mutations that we know either have therapeutic significance or biologic significance. So, the results we receive from these tests generally read out specific mutations in oncogenic genes, or sometimes things like fusions where we have specific targeted drugs. Some of the newer assays can also read out tumor fraction; for example, the newest generation Guardant assay that is methylation-based, they can also quantify tumor fraction. But the disadvantage of the tumor agnostic approach is that it is a little bit less sensitive.
Opposed to that, we have our tumor informed tests, and these require tumor tissue. Essentially, the tumor is sequenced; this can either be whole exome or whole genome sequencing. The newer generation assays are now using whole genome sequencing of the tumor tissue, and a personalized, patient-specific panel of alterations is essentially barcoded on that tumor tissue. This can be either structural variants or it can be mutations, but generally, these are not driver mutations, but sort of things that are present in the tumor tissue that tend to stay unchanged over time. For each particular patient, a personalized assay, if you want to call it a fingerprint or barcode, is created, and then that is what then is used to test the plasma sample. Essentially, you are looking for that specific cancer in the blood, that barcode or fingerprint in the blood. Because of this, this is a much more sensitive way of looking for ctDNA, and obviously, this detects only that particular tumor that was sequenced originally. So, it is much more sensitive and specific to that tumor that was sequenced. You can argue for both approaches in different settings. We use them in different settings because they give us different information. The tumor agnostic approach gives us mutations, which can be used to determine what the next best therapy to use is, while the tumor informed assay is more sensitive, but it is not going to give us information on therapeutic targets. However, it is quantified, and we can follow it over time to see how it changes. We think that it is going to tell us how patients respond to treatment because we see our circulating tumor DNA levels rise and fall as the cancer burden increases or decreases. We decided to use the tumor informed approach in this particular study because we were really interested in how to determine if patients are having response to treatment versus if they are going to progress on their treatment, more so than looking for specific mutations.
Dr. Rafeh Naqash: When you think about these tumor informed assays and you think about barcoding the mutations on the original tumor that you try to track or follow in subsequent blood samples, plasma samples, in your experience, if you have done it in non-lobular cancers, do you think shedding from the tumor has something to do with what you capture or how much you capture?
Dr. Julia Foldi: Absolutely. I think there are multiple factors that go into whether someone has detectable ctDNA or not, and that has to do with the type of cancer, the location, right, where is the metastatic site? This is something that we do not fully understand yet: what are tumors that shed more versus not? There is also clearance of ctDNA, and so how fast that clearance occurs is also something that will affect what you can detect in the blood. ctDNA is very short-lived, only has a half-life of hours, and so you can imagine that if there is little shedding and a lot of excretion, then you are not going to be detecting a lot of it. In general, in the metastatic setting, we see that we can detect ctDNA in a lot of cases, especially when patients are progressing on treatment, because we imagine their tumor burden is higher at that point. Even with the non-tumor informed assays, we detect a lot of ctDNA.
Part of this study was to actually assess: what is the proportion of patients where we can have this information? Because if we are only going to be able to detect ctDNA in less than 50 percent of patients, then it is not going to be a useful method to follow them with. Because this field is new and we have not been using a lot of tumor informed assays in the metastatic setting, we did not really know what to expect when we set out to look at this. We did not know what was going to be the baseline detection rate in this patient population, so that was one of the first things that we wanted to answer.
Dr. Rafeh Naqash: Excellent. Now going to this manuscript in particular, what was the research question, what was the patient population, and what was the strategy that you used to investigate some of these questions?
Dr. Julia Foldi: So, we partnered with Natera, and the reason was that their Signatera tumor-informed assay was the first personalized, tumor-informed, really an MRD assay, minimal residual disease detection assay. It has been around the longest and has been pretty widely used commercially already, even though some of our data is still lacking. but we know that people are using this in the real world. We wanted to gather some real-world data specifically in lobular patients. So, we asked Natera to look at their database of commercial Signatera testing and look for patients with stage 4 lobular breast cancer. The information all comes from the submitting physicians sending in pathologic reports and clinical notes, and so they have that information from the requisitions essentially that are sent in by the ordering physician.
We found 66 patients who were on first-line or close to first-line endocrine-based therapies for their metastatic lobular breast cancer and had serial collections of Signatera tests. The way we defined baseline was that the first Signatera had to be sent within three months of starting treatment. So, it is not truly baseline, but again, this is a limitation of looking at real-world data is that you are not always going to get the best time point that you need. We had over 350 samples from those 66 patients, again longitudinal ctDNA samples, and our first question was what is the baseline detection rate using this tumor informed assay? Then, most importantly, what is the concordance between changes in ctDNA and clinical response to treatment? That is defined by essentially radiologic response to treatment.
Dr. Rafeh Naqash: Interesting. So, what were some of your observations in terms of ctDNA dynamics, whether baseline levels made a difference, whether subsequent levels at different time points made a difference, or subsequent levels at, let us say, cycle three made a difference? Were there any specific trends that you saw?
Dr. Julia Foldi: So, first, at baseline, 95 percent of patients had detectable ctDNA, which is, I think, a really important data point because it tells us that this can be a really useful test. If we can detect it in almost all patients before they start treatment, we are going to be able to follow this longitudinally. And again, these were not true baseline samples. So, I think if we look really at baseline before starting treatment, almost all patients will have detectable ctDNA in the metastatic setting. The second important thing we saw was that disease progression correlated very well with increase in ctDNA. So, in most patients who had disease progression by imaging, we saw increase in ctDNA. Conversely, in most patients who had clinical benefit from their treatment, so they had a response or stable disease, we saw decrease in ctDNA levels. It seems that what we call molecular response based on ctDNA is tracking very nicely along with the radiographic response.
So, those were really the two main observations. Again, this is a small cohort, limited by its real-world nature and the time points that ctDNA assay was sent was obviously not mandated. This is a real-world data set, and so we could not really look at specific time points like you asked about, let us say, cycle three of therapy, right? We did not have all of the right time points for all of the patients. But what we were able to do was to graph out some specific patient scenarios to illustrate how changes in ctDNA correlate with imaging response. I can talk a little bit about that.
Dr. Rafeh Naqash: That was going to be my question. Did you see patients who had serial monitoring using the tumor informed ctDNA assay where the assay became positive a few months before the imaging? Did you have any of those kinds of observations?
Dr. Julia Foldi: Yes, so I think this is where the field is going: are we able to use this technology to maybe detect progression before it becomes clinically apparent? Of course, there are lots of questions about: does that really matter? But it seems like, based on some of the patient scenarios that we present in the paper, that this testing can do that. So, we had a specific scenario, and this is illustrated in a figure in the paper, really showing the treatment as well as the changes in ctDNA, tumor markers, and also radiographic response. So, this particular patient was on first-line endocrine therapy and CDK4/6 inhibitor with palbociclib. Initially, she had a low-level detectable ctDNA. It became undetectable during treatment, and the patient had a couple of serial ctDNA assays that were negative, so undetectable. And then we started, after about seven months on this combination therapy, the ctDNA levels started rising. She actually had three serial ctDNA assays with increasing level of ctDNA before she even had any imaging tests. And then around the time that the ctDNA peaked, this patient had radiographic evidence of progression. There was also an NGS-based assay sent to look for specific mutations at that point. The patient was found to have an ESR1 mutation, which is very common in this patient population. She was switched to a novel oral SERD, elacestrant, and the ctDNA fell again to undetectable within the first couple months of being on elacestrant. And then a very similar thing happened: while she was on this second-line therapy, she had three serial negative ctDNA assays, and then the fourth one was positive. This was two months before the patient had a scan that showed progression again.
Dr. Rafeh Naqash: And Julia, like you mentioned, this is a small sample size, limited number of patients, in this case, one patient case scenario, but provides insights into other important aspects around escalation or de-escalation of therapy where perhaps ctDNA could be used as an integral biomarker rather than an exploratory biomarker. What are some of your thoughts around that and how is the breast cancer space? I know like in GI and bladder cancer, there has been a significant uptrend in MRD assessments for therapeutic decision making. What is happening in the breast cancer space?
Dr. Julia Foldi: So, super interesting. I think this is where a lot of our different fields are going. In the breast cancer space, so far, I have seen a lot of escalation attempts. It is not even necessarily in this particular setting where we are looking at dynamics of ctDNA, but in the breast cancer world, of course, we have a lot of data on resistance mutations. I mentioned ESR1 mutation in a particular patient in our study. ESR1 mutations are very common in patients with ER-positive breast cancer who are on long-term endocrine therapy, and ESR1 mutations confer resistance to aromatase inhibitors. So, that is an area that there has been a lot of interest in trying to detect ESR1 mutations earlier and switching therapy early. So, this was the basis of the SERENA-6 trial, which was presented last year at ASCO and created a lot of excitement. This was a trial where patients had non-tumor-informed NGS-based Guardant assay sent every three to six months while they were on first-line endocrine therapy with a CDK4/6 inhibitor. If they had an ESR1 mutation detected, they were randomized to either continue the same endocrine therapy or switch to an oral SERD. The trial showed that the population of patients who switched to the oral SERD did better in terms of progression-free survival than those who stayed on their original endocrine therapy.
There are a lot of questions about how to use this in routine practice. Of course, it is not trivial to be sending a ctDNA assay every three to six months. The rate of detection of these mutations was relatively low in that study; again, the incidence increases in later lines of therapy. So, there are a lot of questions about whether we should be doing this in all of our first-line patients. The other question is, even the patients who stayed on their original endocrine therapy were able to stay on that for another nine months. So, there is this question of: are we switching patients too early to a new line of therapy by having this escalation approach? So, there are a lot of questions about this. As far as I know, at least in our practice, we are not using this approach just yet to escalate therapy. Time will tell how this all pans out. But I think what is even more interesting is the de-escalation question, and I think that is where tumor informed assays like Signatera and the data that our study generated can be applied.
Actually, our plan is to generate some prospective data in the lobular breast cancer population, and I have an ongoing study to do that, to really be able to tease out the early ctDNA dynamics as patients first start on endocrine therapy. So, this is patients who are newly diagnosed, they are just starting on their first-line endocrine therapy, and measure, with sensitive assays, measure ctDNA dynamics in the first few months of therapy. In those patients who have a really robust response, that is where I think we can really think about de-escalation. In the patients whose ctDNA goes to undetectable after just a few weeks of therapy with just an endocrine agent, they might not even need a CDK4/6 inhibitor in their first-line treatment. So, that is an area where we are very interested in our group, and I know that other groups are looking at this too, to try to de-escalate therapy in patients who clear their ctDNA early on.
Dr. Rafeh Naqash: Thank you so much. Well, lots of questions, but at the same time, progress comes through questions asked, and your project is one of those which is asking an interesting question in a rarer cancer and perhaps will lead to subsequent improvement in how we monitor these individuals and how we escalate or de-escalate therapy. Hopefully, we will get to see more of what you are working on in subsequent submissions to JCO Precision Oncology and perhaps talk more about it in a couple of years and see how the space and field is moving. Thanks again for sharing your insights.
I do want to take one to two quick minutes talking about you as an investigator, Julia. If you could speak to your career pathway, your journey, the pathway to mentorship, the pathway to being a mentor, and how things have shaped for you in your personal professional growth.
Dr. Julia Foldi: Sure, yeah, that is great. Thank you. So, I had a little bit of an unconventional path to clinical medicine. I actually thought I was going to be a basic scientist when I first started out. I got a PhD in Immunology right out of college and was studying not even anything cancer-related. I was studying macrophage signaling in inflammatory diseases, but I was in New York City. This was right around the time that the first checkpoint inhibitors were approved. Actually, some of my friends from my PhD program worked in Jim Allison's lab, who was the basic scientist responsible for ipilimumab. So, I got to kind of first-hand experience the excitement around bringing something from the lab into the clinic that actually changed really the course of oncology. And so, I got very excited about oncology and clinical medicine. So, I decided to kind of switch gears from there and I went back to medical school after finishing my PhD and got my MD at NYU. I knew I wanted to do oncology, so I did a research track residency and fellowship combined at Yale. I started working early on with the breast cancer team there. At the time, Lajos Pusztai was the head of translational research there at Yale, and I started working with him early in my residency and then through my fellowship. I worked on several trials with him, including a neoadjuvant checkpoint inhibitor trial in triple-negative breast cancer patients.
During my last year in fellowship, I received a Conquer Cancer Young Investigator Award to study estrogen receptor heterogeneity using spatial transcriptomics in this subset of breast cancers that have intermediate estrogen receptor expression. From there, I joined the faculty at the University of Pittsburgh in 2022. So, I have been there about almost four years at this point. My interests really shifted slowly from triple-negative breast cancers towards ER-positive breast cancers. When I arrived in Pittsburgh, I started working very closely with some basic and translational researchers here who are very interested in estrogen signaling and mechanisms of resistance to endocrine therapy, and there is a large group here interested in lobular breast cancers.
During my training, I was not super aware even that lobular breast cancer was a unique subtype of breast cancers, and that is, I think, changing a little bit. There is a lot more awareness in the breast cancer clinical and research community about ILC being a unique subtype, but it is not even really part of our training in fellowship, which we are trying to change. But I have become a lot more aware of this because of the research team here and through that, I have become really interested also on the clinical side. And so, we do have a Lobular Breast Cancer Research Center of Excellence here at the University of Pittsburgh and UPMC, and I am the leader on the clinical side. We have a really great team of basic and translational researchers looking at different aspects of lobular breast cancers, and some of the work that I am doing is related to this particular manuscript we discussed and the next steps, as I mentioned, a prospective study of early ctDNA dynamics in lobular patients. I also did some more clinical research work in collaboration with the NSABP looking at long-term outcomes of patients with lobular versus ductal breast cancers in some of their older trials. And so, that is, in a nutshell, a little bit about how I got here and how I became interested in ILC.
Dr. Rafeh Naqash: Well, thank you for sharing those personal insights and personal journey. I am sure it will inspire other trainees, fellows, and perhaps junior faculty in trying to find their niche. The path, as you mentioned, is not always straight; it often tends to be convoluted. And then finding an area that you are interested in, taking things forward, and being persistent is often what matters.
Dr. Julia Foldi: Thank you so much for having me. It was great.
Dr. Rafeh Naqash: It was great chatting with you.
And thank you for listening to JCO Precision Oncology Conversations. Don't forget to give us a rating or review, and be sure to subscribe so you never miss an episode. You can find all ASCO shows at asco.org/podcasts.
The purpose of this podcast is to educate and to inform. This is not a substitute for professional medical care and is not intended for use in the diagnosis or treatment of individual conditions.
Guests on this podcast express their own opinions, experience, and conclusions. Guest statements on the podcast do not express the opinions of ASCO. The mention of any product, service, organization, activity, or therapy should not be construed as an ASCO endorsement.

In this JCO Precision Oncology Article Insights episode, host Dr. Jiasen He summaries the article, "Longitudinal Evaluation of Circulating Tumor DNA as a Prognostic Biomarker to Detect Molecular Residual Disease in Germ Cell Tumors," by Hassoun et al.
TRANSCRIPT
Jiasen He: Hello, and welcome to the JCO Precision Oncology Article Insights. I'm your host, Jiasen He, and today, we'll be discussing the JCO Precision Oncology article, "Longitudinal Evaluation of Circulating Tumor DNA as a Prognostic Biomarker to Detect Molecular Residual Disease in Germ Cell Tumors," by Dr. Rebecca Hassoun and colleagues.
Traditionally, treatment response for solid tumors has relied on imaging, which focuses on visible anatomic changes in the tumor. However, imaging does not always reflect molecular or cellular changes and cannot detect microscopic disease, which is clinically important and often linked to relapse. Liquid biopsy, on the other hand, is minimally invasive and can be used for cancer monitoring by analyzing circulating biomarkers in biofluids such as blood.
One type of liquid biopsy is circulating tumor DNA, or ctDNA, which measures small fragments of DNA released by tumor cells into the bloodstream. ctDNA can allow precise monitoring of tumor-specific mutations and be a powerful tool for assessing treatment responses. ctDNA has already been applied in clinical settings for cancers such as non-small cell lung cancer and breast cancer, etcetera. However, there is still limited data on the use of ctDNA for germ cell tumors.
Germ cell tumors are the most common malignancy affecting men aged 15 to 35 years. Accurate risk stratification and disease monitoring is key to risk-adapted therapy, maximizing the chance of cure while minimizing side effects. One unique tool we use currently for diagnosis, staging, and monitoring is serum tumor markers, such as AFP, beta-hCG, and LDH. However, these markers have limitations, including false elevation in certain clinical scenarios, and studies have shown that they can be normal in up to 40 percent of patients with germ cell tumor. This creates an unmet need for other sensitive and specific biomarkers to improve patient care.
In this paper, the authors investigated the use of ctDNA in a cohort of patients with germ cell tumor at various disease time points. They compared ctDNA results with traditional serum tumor markers to evaluate whether ctDNA can predict relapse and survival outcomes. This multi-institutional retrospective study included patients with stage I, II, and III germ cell tumors, primarily testicular cancer, who had at least one ctDNA test result.
ctDNA was evaluated longitudinally at different time points, including pre-orchiectomy, during the molecular residual disease, or MRD, window, defined as 1 to 12 weeks post-orchiectomy but before primary therapy, and during the surveillance window, defined as more than 12 weeks post-orchiectomy or follow retroperitoneal lymph node dissection or post-chemotherapy. ctDNA analysis was performed using a tumor-informed 16 multiplex PCR next-generation sequencing assay.
A total of 324 plasma samples were analyzed from 74 patients in this cohort. The majority had stage I disease, around 40 percent, and nonseminomatous histology, around 70 percent. 15 patients were evaluated in the pre-orchiectomy window, and only one patient tested negative for ctDNA. This patient had stage I disease. The authors further assessed ctDNA positivity in both the MRD window and surveillance window, evaluating its association with event-free survival.
They found that ctDNA outperformed serum tumor markers in both settings. ctDNA positivity was associated with significantly worse event-free survival compared with ctDNA-negative patients. Among the 14 patients with stage II to III disease who had ctDNA assessed in both the MRD window and surveillance window, nine patients consistently had a negative ctDNA or converted from positive to negative over time. In contrast, five patients demonstrated persistent ctDNA positivity, and all of these patients subsequently relapsed.
Among the 38 patients who had both ctDNA and serum tumor marker tests during the MRD window, nine patients showed discordant biomarker results. Of these, 6 patients were ctDNA-negative but serum tumor marker-positive, and one of them experienced recurrence. Three patients were ctDNA-positive but serum tumor marker-negative, and one of these patients also recurred. During the surveillance window, 46 patients had both biomarkers available, and 10 showed discordant results. Three patients were ctDNA-negative but serum tumor marker-positive, and none of them recurred. In contrast, all seven patients who were ctDNA-positive but serum tumor marker-negative experienced recurrence.
This intriguing data strongly support the potential role of ctDNA in patients with stage I, II, and III germ cell tumors. However, as the authors noted, the retrospective nature of the study presents limitations, as treatment approaches, imaging schedules, and the timing of testing were not standardized, and ctDNA testing varies among participating institutions. Larger prospective trials with standardized protocols and long-term follow-up will be essential to validate these findings and determine how ctDNA can be reliably integrated into clinical practice.
Thank you for tuning in to JCO Precision Oncology Article Insights. Don't forget to subscribe and join us next time as we explore more groundbreaking research shaping the future of oncology.
The purpose of this podcast is to educate and to inform. This is not a substitute for professional medical care and is not intended for use in the diagnosis or treatment of individual conditions. 
Guests on this podcast express their own opinions, experience, and conclusions. Guest statements on the podcast do not express the opinions of ASCO. The mention of any product, service, organization, activity, or therapy should not be construed as an ASCO endorsement.

JCO PO author Dr. Wainberg at UCLA shares insights into the JCO PO article, "Prevalence of FGFR2b Protein Overexpression in Advanced Gastric Cancers During Prescreening for the Phase III FORTITUDE-101 Trial." Host Dr. Rafeh Naqash and Dr. Wainberg discuss how FGFR2b prevalence was similar across geographic regions and within defined patient and sample variables regardless of the level of expression.
TRANSCRIPT TO COME

In this JCO Precision Oncology Article Insights episode, host Dr. Harold Nathan Tan summarizes "Palbociclib in Patients With Head and Neck Cancer and Other Tumors With CDKN2A Alterations: Results From the Targeted Agent and Profiling Utilization Registry Study" by Worden et al. 
TRANSCRIPT
Harold Nathan Tan: Welcome to JCO Precision Oncology Article Insights, where we explore research that is reshaping our understanding of cancer therapeutics. I'm your host, Harold Nathan Tan, and today's episode centers on the TAPUR study, an analysis that confronts a long-standing assumption in molecular oncology: namely, whether CDKN2A alterations create a therapeutic vulnerability that can be exploited by CDK4/6 inhibition with palbociclib.
CDKN2A is one of the most frequently altered tumor suppressors across solid tumors. Its importance lies in its production of two proteins, p16 and p14, which serve as guardians of cell cycle progression. p16 directly inhibits CDK4 and CDK6, preventing phosphorylation of the RB protein and therefore blocking entry into S phase, whereas p14 stabilizes p53 by counteracting MDM2, enabling cells to pause or die in response to oncogenic stress. When CDKN2A is lost or mutated, these dual checkpoints collapse. CDK4/6 activity becomes unchecked, RB remains phosphorylated and inactive, and p53-mediated surveillance is blunted from a mechanistic standpoint. This creates a possible dependency on CDK4/6 signaling that could, in principle, be therapeutically reversed by palbociclib.
The TAPUR study is a prospective phase 2 basket study designed to evaluate whether FDA-approved targeted agents can meaningfully benefit patients with advanced treatment-refractory cancers harboring specific genomic alterations. In this analysis, patients were eligible for palbociclib if their tumors carried CDKN2A loss or mutation and retained RB activity. Two cohorts were examined: one consisting of head and neck cancers, and another composed of a broad spectrum of tumor types that collectively shared the CDK2 alteration.
The results from the head and neck cancer cohort are particularly intriguing. Among the 28 available patients, the study observed a disease control rate of 40%, surpassing the predefined threshold for a positive signal. Although the objective response rate was low at only 4% with one partial response, the durability of disease stabilization was clinically meaningful. However, the most important insight comes from examining which head and neck tumors benefited. The strongest and most durable disease control occurred in non-squamous malignancies, particularly salivary gland tumors such as adenocarcinoma, adenoid cystic carcinoma, and poorly differentiated parotid tumors, as well as in esthesioneuroblastoma.
In contrast, classic head and neck squamous cell carcinoma rarely demonstrated sustained benefit. When progression-free survival was analyzed, non-squamous tumors achieved a median PFS of approximately 20 weeks compared to just eight weeks in squamous tumors. This divergence reflects deep biological differences. Many non-squamous head and neck cancers preserve an intact RB axis and rely on CDK4/6-driven cell cycle control as a core proliferative mechanism. By contrast, squamous tumors tend to accumulate a dense array of co-alterations that weaken or circumvent CDK4/6 dependency. Many squamous tumors also harbor disruptive TP53 mutations, removing essential checkpoint control and allowing the cell to bypass the growth-arresting effects of palbociclib. In other words, even though CDKN2A loss is present, CDK4/6 is no longer the dominant node controlling proliferation in these cancers, and the tumor simply finds other ways to drive cell cycle entry.
One of the most thought-provoking findings from the TAPUR study involves esthesioneuroblastoma. Three patients with this rare tumor achieved durable disease control despite the lack of standardized systemic treatment options for this malignancy. Genomic analyses have shown that while esthesioneuroblastoma often carries TP53 or IDH2 mutations, a meaningful subset exhibits alterations in CDKN2A or related cell cycle regulators. The consistency of this disease stabilization observed in TAPUR may reflect a lineage-specific reliance on CDK4/6 signaling, opening the door for future exploration of CDK4/6 inhibitors in this orphan disease.
In the histology-pooled cohort, which included 40 available patients across 18 tumor types, palbociclib did not achieve the disease control threshold required to declare activity, with only a disease control rate of 13% and an ORR of 5%. While a few isolated responses occurred, for instance in thymic carcinoma and B-cell lymphoma, the overall disease control rate was 13%, which failed to rise above what might be expected from the natural history of advanced refractory cancers. This outcome reinforces the principle that CDKN2A loss is not a universal predictor of CDK4/6 dependency. Many of the tumors represented in this cohort, such as pancreatic cancer, melanoma, and gastrointestinal malignancies, are well known to evolve multiple compensatory mechanisms that circumvent CDK4/6 as a critical proliferative node.
The safety profile of palbociclib was consistent with its known hematologic toxicities. High rates of neutropenia, leukopenia, and thrombocytopenia were observed, along with one treatment-related death due to respiratory failure. In a setting where activity is limited to specific subgroups, these toxicities underscore the importance of careful patient selection and raise the bar for demonstrating clinically meaningful benefit, particularly in heavily pretreated populations.
So what do these findings tell us about the broader landscape of precision oncology? First, they remind us that a mutation's functional role is dependent on the cellular and lineage context in which it occurs. CDKN2A loss may accelerate proliferation in many tumors, but the mechanism of that acceleration varies widely, and the degree to which a tumor relies on CDK4/6 signaling is anything but uniform. Second, the findings suggest that palbociclib monotherapy may hold meaningful and durable benefit in the subset of non-squamous head and neck cancers, particularly salivary gland malignancies and esthesioneuroblastoma.
Third and perhaps most importantly, the results reinforce a growing consensus that the future of CDK4/6 inhibition in solid tumors lies not in monotherapy, but in rational combination strategies. CDK4/6 inhibitors have been shown to synergize with EGFR inhibitors, PIK3CA, and mTOR inhibitors, MEK inhibition, and even immune checkpoint blockade. These combinations aim to dismantle the compensatory pathways that allow tumors to escape CDK4/6 blockade and may unlock therapeutic potential in tumors that show limited sensitivity to monotherapy.
Ultimately, the TAPUR findings challenge the notion that CDKN2A is a straightforward predictive biomarker. Instead, the study reveals CDKN2A as a biomarker whose meaning is modulated by tumor lineage, co-mutation status, and the broader regulatory circuit governing proliferation. Precision oncology must therefore move beyond single-gene interpretation towards integrated frameworks that situate genomic alterations within their biologic ecosystems. In some head and neck cancer subtypes, particularly non-squamous malignancies, that ecosystem appears amenable to CDK4/6 inhibition, and that insight, not the simplistic gene-to-drug match, represents the true value of the TAPUR analysis.
Thank you for joining me for this episode of JCO Precision Oncology Article Insights. I'm Harold Nathan Tan, and I look forward to exploring more research that continues to refine how we understand and strategically exploit the vulnerabilities of cancer.
The purpose of this podcast is to educate and to inform. This is not a substitute for professional medical care and is not intended for use in the diagnosis or treatment of individual conditions.
Guests on this podcast express their own opinions, experience, and conclusions. Guest statements on the podcast do not express the opinions of ASCO. The mention of any product, service, organization, activity, or therapy should not be construed as an ASCO endorsement.

JCO PO author Dr. Shilpa Gupta at Cleveland Clinic Children's Hospital shares insights into her article, "Fibroblast Growth Factor Receptor 3 (FGFR3) Alteration Status and Outcomes on Immune Checkpoint Inhibitors (ICPI) in Patients with Metastatic Urothelial Carcinoma". Host Dr. Rafeh Naqash and Dr. Gupta discuss how FGFR3 combined with TMB emerged as a biomarker that may be predictive for response to ICPI in mUC.
TRANSCRIPT
Dr. Rafeh Naqash: Hello and welcome to JCO Precision Oncology Conversations, where we bring you engaging conversations with authors of clinically relevant and highly significant JCO PO articles. I'm your host, Dr. Rafeh Naqash, podcast editor for JCO Precision Oncology and Associate Professor at the OU Health Stephenson Cancer Center.
Today I am excited to be joined by Dr. Shilpa Gupta, Director of Genitourinary Medical Oncology at the Cancer Institute and co-leader of the GU Oncology Program at the Cleveland Clinic, and also lead author of the JCO PO article titled "Fibroblast Growth Factor Receptor 3 Alteration Status and Outcomes on Immune Checkpoint Inhibitors in Patients With Metastatic Urothelial Carcinoma."
At the time of this recording, our guest's disclosures will be linked in the transcript.
Shilpa, welcome again to the podcast. Thank you for joining us today.
Dr. Shilpa Gupta: Thank you, Rafeh. Honor to be here with you again.
Dr. Rafeh Naqash: It is nice to connect with you again after two years, approximately. I think we were in our infancy of our JCO PO podcast when we had you first time, and it has been an interesting journey since then.
Dr. Shilpa Gupta: Absolutely.
Dr. Rafeh Naqash: Well, excited to talk to you about this article that you published. Wanted to first understand what is the genomic landscape of urothelial cancer in general, and why should we be interested in FGFR3 alterations specifically?
Dr. Shilpa Gupta: Bladder cancer or urothelial cancer is a very heterogeneous cancer. And while we find there is a lot of mutations can be there, you know, like BRCA1, 2, in HER2, in FGFR, we never really understood what is driving the cancer. Like a lot of old studies with targeted therapies did not really work. For example, we think VEGF can be upregulated, but VEGF inhibitors have not really shown definite promise so far.
Now, FGFR3 receptor is the only therapeutic target so far that has an FDA approved therapy for treating metastatic urothelial cancer patients, and erdafitinib was approved in 2019 for patients whose tumors overexpressed FGFR3 mutations, alterations, or fusions. And in the landscape of bladder cancer, it is important because in patients with non-muscle invasive bladder cancer, about 70 to 80% patients can have this FGFR3. But as patients become metastatic, the alterations are seen in, you know, only about 10% of patients. So the clinical trials that got the erdafitinib approved actually used archival tumor from local cancer. So when in the real world, we don't see a lot of patients if we are trying to do metastatic lesion biopsies. And why it is important to know this is because that is the only targeted therapy available for our patients right now.
Dr. Rafeh Naqash: Thank you for giving us that overview. Now, on the clinical side, there is obviously some interesting data for FGFR3 on the mutation side and the fusion side. In your clinical practice, do you tend to approach these patients differently when you have a mutation versus when you have a fusion?
Dr. Shilpa Gupta: We can use the treatment regardless of that.
Dr. Rafeh Naqash: I recently remember I had a patient with lung cancer, squamous lung cancer, who also had a synchronous bladder mass. And the first thought from multiple colleagues was that this is metastatic lung. And interestingly, the liquid biopsy ended up showing an FGFR3-TACC fusion, which we generally don't see in squamous lung cancers. And then eventually, I was able to convince our GU colleagues, urologists, to get a biopsy. They did a transurethral resection of this tumor, ended up being primary urothelial and synchronous lung, which again, going back to the FGFR3 story, I saw in your paper there is a mention of FGFR3-TACC fusions. Anything interesting that you find with these fusions as far as biology or tumor behavior is concerned?
Dr. Shilpa Gupta: We found in our paper of all the patients that were sequenced that 20% had the pathognomonic FGFR3 alteration, and the most common were the S249C, and the FGFR3-TACC3 fusion was in 45 patients. And basically I will say that we didn't want to generate too much as to fusion or the differences in that.
The key aspect of this paper was that historically there were these anecdotal reports saying that patients who have FGFR alterations or mutations, they may not respond well to checkpoint inhibitors because they have the luminal subtype. And these were backed by some preclinical data and small anecdotal reports. But since then, we have seen that, and that's why a lot of people would say that if somebody's tumor has FGFR3, don't give them immunotherapy, give them erdafitinib first, right?
So then we had this Phase 3 trial called the THOR trial, which actually showed that giving erdafitinib before pembrolizumab was not better. That debunked that myth, and we are actually reiterating that because in our work we found that patients who had FGFR3 alterations or fusions, and if they also have TMB-high, they actually respond very well to single agent immunotherapy. And that is, I think, very important because it tells us that we are not really seeing that so-called potential of resistance to immunotherapy in these patients. So to answer your question, yeah, we did see those differences, but I wouldn't say that any one marker is more prominent.
Dr. Rafeh Naqash: The analogy is kind of similar to what we see in lung cancer with these mutations called STK11/KEAP1, which are also present in some other tumors. And one of the questions that I don't think has been answered is when you have in lung cancer, if you extrapolate this, where doublet or single agent immunotherapy doesn't do as well in tumors that are STK11 mutated. But then if you have a high TMB, question is does that TMB supersede or trump the actual mutation? Could that be one reason why you see the TMB-high but FGFR3 altered tumors in your dataset responding or having better outcomes to immunotherapy where potentially there is just more neoantigens and that results in a more durable or perhaps better response to checkpoint therapy?
Dr. Shilpa Gupta: It could be. But you know, the patients who have FGFR alterations are not that many, right? So we have already seen that just patients with TMB-high respond very well to immunotherapy. Our last podcast was actually on that, regardless of PD-L1 that was a better predictor of response to immunotherapy. So I think it's not clear if this is adding more chances of response or not, because either way they would respond. But what we didn't see, which was good, that if they had FGFR3, it's not really downplaying the fact that they have TMB-high and that patients are not responding to immunotherapy. So we saw that regardless, and that was very reassuring.
Dr. Rafeh Naqash: So if tomorrow in your clinic you had an individual with an FGFR3 alteration but TMB-high, I guess one could be comfortable just going ahead with immunotherapy, which is what the THOR trial as you mentioned.
Dr. Shilpa Gupta: Yes, absolutely. And you know, when you look at the toxicity profiles of pembrolizumab and erdafitinib, really patients really struggle with using the FGFR3 inhibitors. And of course, if they have to use it, we have to, and we reserve it for patients. But it's not an easy drug to tolerate. Currently the landscape is such that, you know, frontline therapy has now evolved with an ADC and immunotherapy combinations. So really if patients progress and have FGFR3 alterations, we are using erdafitinib. But let's say if there were a situation where a patient has had chemotherapy, no immunotherapy, and they have FGFR3 upregulation and TMB-high, yes, I would be comfortable with using only pembrolizumab. And that really ties well together what we saw in the THOR trial as well.
Dr. Rafeh Naqash: Going to the clinical applications, you mentioned a little bit of this in the manuscript, is combination therapies. You alluded to it a second back. Everything tends to get combined with checkpoint therapy these days, as you've seen with the frontline urothelial, pembrolizumab with an ADC. What is the landscape like as far as some of these FGFR alterations are concerned? Is it reasonable to combine some of those drugs with immune checkpoint therapy? And what are some of the toxicity patterns that you've potentially seen in your experience?
Dr. Shilpa Gupta: So there was indeed a trial called the NORSE trial. It was a randomized trial but not a comparative cohort, where they looked at FGFR altered patients. And when they combined erdafitinib plus cetrelimab, that did numerically the response rates were much higher than those who got just erdafitinib. So yeah, the combination is definitely doable. There is no overlapping toxicities.
But unfortunately that combination has not really moved forward to a Phase 3 trial because it's so challenging to enroll patients with such kind of rare mutations on large trials, especially to do registration trials. And since then the frontline therapy has evolved to enfortumab vedotin and pembrolizumab. I know there is an early phase trial looking at a next generation FGFR inhibitor. There is a triplet combination looking in Phase 1 setting with a next generation FGFR inhibitor with EV-pembro. However, it's not a randomized trial. So you know, I worry about such kinds of combinations where we don't have a path for registration.
And in the four patients that have been treated, four or five patients in the early phase as a part of basket trial, the toxicities were a lot, you know, when you combine the EV-pembro and an FGFR3 inhibitor, we see more and more toxicity. So the big question is do we really need the "kitchen sink" approach when we have a very good doublet, or unless the bar is so high with the doublet, like what are we trying to add at the expense of patient toxicity and quality of life is the big question in my mind.
Dr. Rafeh Naqash: Going back to your manuscript specifically, there could be a composite biomarker. You point out like FGFR in addition to FGFR TMB ends up being predictive prognostic there. So that could potentially be used as an approach to stratify patients as far as treatment, whether it's a single agent versus combination. Maybe the TMB-low/FGFR3 mutated require a combination, but the TMB-high/FGFR mutated don't require a combination, right?
Dr. Shilpa Gupta: No, that's a great point, yeah.
Dr. Rafeh Naqash: But again, very interesting, intriguing concepts that you've alluded to and described in this manuscript.
Now, a quick take on how things have changed in the bladder cancer space in the last two years. We did a podcast with you regarding some biomarkers as you mentioned two years back. So I really would like to spend the next minute to two to understand how have things changed in the bladder cancer space? What are some of the exciting things that were not there two years back that are in practice now? And how do you anticipate the next two years to be like? Maybe we'll have another podcast with you in another two years when the space will have changed even more.
Dr. Shilpa Gupta: Certainly a lot has happened in the two years, you know. EV-pembro became the universal frontline standard, right? We have really moved away from cisplatin eligibility in metastatic setting because anybody would benefit from EV-pembro regardless of whether they are candidates for cisplatin or not, which historically was relevant. And just two days ago, we saw that EV-pembro has now been approved for localized bladder cancer for patients who are cisplatin ineligible or refusing. So, you know, this very effective regimen moving into earlier setting, we now have to really think of good treatment options in the metastatic setting, right? So I think that's where a lot of these novel combinations may come up.
And what else we've seen is in a tumor agnostic trial called the DESTINY-PanTumor trial, patients who had HER2 3+ on immunohistochemistry, we saw the drug approval for T-DXd, and I think that has kind of reinvigorated the interest in HER2 in bladder cancer, because in the past targeting HER2 really didn't work. And we still don't know if HER2 is a driver or not. And at ESMO this year, we saw an excellent study coming out of China with DV which is targeting HER2, and toripalimab, which is a Chinese checkpoint inhibitor, showing pretty much similar results to what we saw with EV-pembro.
Now, you know, not to do cross-trial comparisons, but that was really an amazing, amazing study. It was in the presidential session. And I think the big question is: does that really tell us that HER2-low patients will not benefit? Because that included 1+, 2+, 3+. So that part we really don't know, and I think we want to study from the EV-302 how the HER2 positive patients did with EV and pembro. So that's an additional option, at least in China, and hopefully if it gets approved here, there is a trial going on with DV and pembro.
And lastly, we've seen a very promising biomarker, like ctDNA, for the first time in bladder cancer in the adjuvant setting guiding treatment with adjuvant atezolizumab. So patients who were ctDNA positive derived overall survival and recurrence-free survival benefit. So that could help us select moving forward with more studies. We can spare unnecessary checkpoint inhibitors in patients who are not going to benefit.
So I think there is a lot happening in our field, and this will help do more studies because we already have the next generation FGFR inhibitors which don't have the toxicities that erdafitinib comes with. And combining those with these novel ADCs and checkpoint inhibitors, you know, using maybe TMB as a biomarker, because we really need to move away from PD-L1 in bladder cancer. It's shown no utility whatsoever, but TMB has.
Dr. Rafeh Naqash: Well, thank you so much, Shilpa, for that tour de force of how things have changed in bladder cancer. There used to be a time when lung and melanoma used to lead this space in terms of the number of approvals, the biomarker development. It looks like bladder cancer is shifting the trend at this stage. So definitely exciting to see all the new changes that are coming up.
I'd like to spend another minute and a half on your career. You've obviously been a leader and example for many people in the GU space and beyond. Could you, for the sake of our early career especially, the trainees and other listeners, describe how you focused on things that you're currently leading as a leader, and how you shaped your career trajectory over the last 10 years?
Dr. Shilpa Gupta: That's a really important question, Rafeh, and you and I have had these discussions before, you know, being an IMG on visas like you, and being in different places. I think I try to make the most of it, you know, instead of focusing on the setbacks or the negative things. Like tried to grab the opportunities that came along. When I was at Moffitt, got to get involved with the Phase 1 trial of pembrolizumab in different tumor types. And just keeping my options open, you know, getting into the bladder cancer at that time when I wanted to really do only prostate, but it was a good idea for me to keep my options open and got all these opportunities that I made use of.
I think an important thing is to, like you said, you know, have a focus. So I am trying to focus more on biomarkers that, you know, we know that 70% patients will respond to EV-pembro, right? But what about the remaining 30%? Like, so I'm really trying to understand what determines hyperprogressors with such effective regimens who we really struggle with in the clinic. They really don't do well with anything we give them after that. So we are doing some work with that and also trying to focus on PROs and kind of patient-reported outcomes.
And a special interest that I've now developed and working on it is young-onset bladder cancer. You know, the colorectal cancer world has made a lot of progress and we are really far behind. And bladder cancer has historically been a disease of the elderly, which is not the case anymore. We are seeing patients in their 30s and 40s. So we launched this young-onset bladder cancer initiative at a Bladder Cancer Advocacy Network meeting and now looking at more deep dive and creating a working group around that.
But yeah, you know, I would say that my philosophy has been to just take the best out of the situation I'm in, no matter where I am. And it has just helped shape my career where I am, despite everything.
Dr. Rafeh Naqash: Well, thank you again. It is always a pleasure to learn from your experiences and things that you have helped lead. Appreciate all your insights, and thank you for publishing with JCO PO. Hopefully we will see more of your biomarker work being published and perhaps bring you for another podcast in a couple of years.
Dr. Shilpa Gupta: Yeah, thank you, Rafeh, for the opportunity. And thanks to JCO PO for making these podcasts for our readers. So thanks a lot.
Dr. Rafeh Naqash: Thank you for listening to JCO Precision Oncology Conversations. Don't forget to give us a rating or review and be sure to subscribe so you never miss an episode. You can find all ASCO shows at asco.org/podcast.
The purpose of this podcast is to educate and to inform. This is not a substitute for professional medical care and is not intended for use in the diagnosis or treatment of individual conditions.
Guests on this podcast express their own opinions, experience, and conclusions. Guest statements on the podcast do not express the opinions of ASCO. The mention of any product, service, organization, activity, or therapy should not be construed as an ASCO endorsement.


DISCLOSURES

Dr. Shilpa Gupta
Stock and Other Ownership Interests:
Company: BioNTech SE,  Nektar
Consulting or Advisory Role:
Company: Gilead Sciences, Pfizer, Merck, Foundation Medicine, Bristol-Myers Squibb/Medarex, Natera, Astellas Pharma, AstraZeneca, Novartis, Johnson & Johnson/Janssen
Research Funding:
Recipient: Your Institution
Company: Bristol Myers Squibb Foundation, Merck, Roche/Genentech, EMD Serono, Exelixis, Novartis, Tyra Biosciences, Pfizer, Convergent Therapeutics, Acrivon Therapeutics, Flare Therapeutics, Amgen

Travel, Accommodations, Expenses:
Company: Pfizer, Astellas Pharma, Merck