Pembrolizumab in Patients With Advanced Cancers With HTMB

Dr. Shannon Westin and her guests, Dr. Herbert Duvivier and Dr. Richard Schilsky, discuss the paper “Pembrolizumab in Patients With Tumors With High Tumor Mutational Burden: Results From the Targeted Agent and Profiling Utilization Registry Study” published in the JCO.

TRANSCRIPT

The guest on this podcast episode has no disclosures to declare. 

Shannon Westin: Hello, everyone, and welcome to another episode of JCO After Hours, the podcast where we get in-depth into articles published in the Journal of Clinical Oncology. I am your host, Shannon Westin, GYN Oncologist and Social Media Editor of the JCO. As always, it is my pleasure to serve and bring this information to you. 

Today, we will be discussing, “Pembrolizumab in Patients With Tumors With High Tumor Mutational Burden: Results From the Targeted Agent and Profiling Utilization Registry Study.” And this was published in the JCO on August 10th, 2023. 

None of the authors have any conflicts of interest to disclose. 

Joining me today are two of the authors, Dr. Herbert Duvivier, the principal investigator of this arm of the TAPUR trial. Welcome.

Dr. Herbert Duvivier: Thank you. 

Shannon Westin: And then, of course, many of you know Dr. Richard Schilsky, who is the former CMO and Executive Vice President of ASCO and a principal investigator on the TAPUR study.  

Dr. Richard Schilsky: Thank you, Shannon. 

Shannon Westin: So, let's get going. I think the first thing would be great is to level set and make sure everyone knows exactly what this TAPUR basket trial is, the Targeted Agent and Profiling Utilization Registry study. Can you guys give the audience a brief description of the objective of TAPUR and maybe how it came to fruition? 

Dr. Richard Schilsky: Sure. This is Richard Schilsky. Maybe I can start with that. The TAPUR study is a prospective, phase II, multi-basket, multi-center genomic-matching trial. Its primary objective is to identify signals of drug activity for targeted agents that are already marketed. But in the TAPUR study they are being used outside of their FDA-approved indication. The study, as you may know, was conceived in 2014, launched in 2016, and is still enrolling patients across the country. Really, the genesis of the study came from the fact that it began at the time where genomic profiling of patients with advanced cancer was becoming more commonplace. Genomic alterations that could be targeted by already marketed drugs were being identified. However, patients and doctors were having difficulty accessing these drugs because they were not used on label and were unlikely to be covered by insurance. And moreover, even if they could access the drugs, there was no organized mechanism to collect outcome data and report on the results of the patient experience receiving that treatment. 

So those factors led to the development of TAPUR, which attempts to solve both the drug access problem by having collaborating pharmaceutical companies donate their drugs to the trial so they’re available to patients at no cost, but also implements a structured data collection mechanism so all of the relevant clinical outcomes with the patients can be collected and ultimately reported. And that’s how TAPUR came about.

Shannon Westin: Well, it was so necessary, and I think we do so much of our oncology treatments off-label, but as we get more and more expensive drugs when we move away from chemotherapies and more targeted immunotherapies, it’s very hard to get those drugs off label. So this was such a relevant and necessary trial that had to happen, and it's a great example of leadership that you had the vision to put this together through ASCO. 

I think the natural next question for me is having not put patients on the TAPUR study, how does a patient join this study? How do they get started? Walk us through that.

Dr. Herbert Duvivier: At our institution, normally, all the physicians are aware of the TAPUR trial through internal conversations. When they have patients who have been treated with multiple lines of standard therapy, usually the next step for them is to get NGS testing. We have a research team that reviews all NGS testing for these patients and knows the open arms of the TAPUR trial. And if there happens to be a particular patient who may match with one, they will inform the physician. It is then up to the physician to speak to the patient about that option. 

Shannon Westin: Do you have people come looking for the TAPUR trial or are these generally more established patients?

Dr. Herbert Duvivier: From my perspective, I think it is usually established patients.

Shannon Westin: I think what I love about this trial, and I have spoken about this trial in lectures around baskets, it’s such a pragmatic design making it as straightforward as possible to really implement across different centers, whether academic or community, or wherever they are. I guess one of the questions always around these targeted therapies is the molecular selection. How do you make sure that people are being appropriately molecularly selected and how do you decide which testing to utilize? 

Dr. Richard Schilsky: As you pointed out, Dr. Westin, the goal of the study from the beginning was to have a very pragmatic design, in a sense to have this study attempt to replicate the way oncologists were deploying precision medicine in their practice. The study has broad eligibility criteria, it has minimum necessary data collection, it uses conventional clinical evaluations, there are no additional clinical evaluations required that are not part of routine clinical care. And it just makes it easy to embed the study into the clinical workflow. The study is based largely at community sites, about 85% of the 268 participating sites are located in smaller communities. The study has a set of genomic matching rules that are listed in the protocol and baked into the IT platform for the study as a rules engine. For every treatment available in TAPUR, there is a set of genomic inclusion and exclusion criteria. 

So in essence the way it works, the physician determines that NGS testing is appropriate for their patient and can use any NGS test they want, as long as the test is performed in a CLIA certified, CAP, or New York State-accredited laboratory. They select the test, they select the biospecimen to be tested, they get the results, they look at the results, and they determine if there is a genomic alteration in the patient's tumor that is targeted by one of the study treatments in the TAPUR study. They can enter that into the rules engine, the rules engine will confirm or not that the appropriate alteration of treatment has been selected. If it is confirmed, then the patient can immediately be enrolled in the study if they meet the clinical inclusion and exclusion criteria. 

If the rules engine does not confirm the treatment match is appropriate, or in some cases there are multiple possible treatment matches, if there are multiple alterations that can be targeted, or another case is the doctor is simply uncertain about which alteration is best to target, then the clinical site can send that patient case to the TAPUR molecular tumor board. A group of experts convenes weekly that reviews the clinical history, the pathology report, genomic test report, the prior therapy the patient has received, and they make a determination as to whether or not there is an appropriate therapy that’s available on TAPUR for the patient. And if not, then are there other potential therapies  that are available that could be considered. That information is sent back to the treating physician who determines whether or not here she feels that treatment option is appropriate for their patient, and if so, the patient can then be enrolled and receive the therapy.

Shannon Westin: So awesome. I love the idea. If we don’t have an arm for you on our trial, we can help assist you potentially determine an option for your patient outside of that. That’s so clever. 

Okay. So let’s get into this particular arm. Obviously, our audience is quite savvy and are aware of the role of immune checkpoint inhibition across a number of solid tumors. Could you describe what you sought to determine in this particular arm of the TAPUR study? 

Dr. Herbert Duvivier: I think one of the most important things to remember about this study is that this study was opened and accruing prior to pembrolizumab becoming FDA approved in, I think, June of 2020. So prior to June of 2020, there was no indication for pembrolizumab in high TMB tumor types and the goal of the study was to determine if pembrolizumab had any overall response rate, duration of responses, progression-free survival, or overall survival advantage over what would be considered standard chemotherapy at that time in patients with high TMB.

Dr. Richard Schilsky: Yeah, that's exactly right. And in this paper that we're discussing, we're reporting on two different groups of patients. So there's a group of 28 patients, all with colorectal cancer, all of whom had high tumor mutation burden, as defined by the protocol. And that's one group. Then there's a second, larger group of patients, which is a very heterogeneous group of solid tumor patients. And the reason that that group is reported is there were patients who were being enrolled with multiple different tumor types with high tumor mutation burden. Each tumor type determined a specific, tumor-specific cohort in the study, and they were enrolling at different rates depending upon how common the particular tumor type was. But once the FDA approval for pembrolizumab, for any tumor with a high tumor mutation burden, was granted, then all of those cohorts essentially had to close to new enrollments because there was no longer an off-label use for pembrolizumab in that setting - everything was now on the label. 

The result was that we then basically collapsed all of the open cohorts that were not then going to be able to complete into this one large, heterogeneous cohort that's being reported in this paper. And going back to the colorectal results, in the paper, we describe a disease control rate of 31%, an objective response rate of 11%. There were three patients who had partial responses lasting 12, 27, and 97 weeks each. And I think it's important to point out that in this particular cohort, essentially all of the colon cancer patients were microsatellite stable. So that's an interesting nuance here because we know that pembrolizumab is active and has an FDA approval in microsatellite high tumors. But this particular group of patients was essentially all microsatellite stable, suggesting that even in that population, if the tumor also has a high tumor mutation burden, the patient has the potential to respond and benefit from the treatment.

Shannon Westin: I found that very intriguing. And, of course, as a gynecologic oncologist that treats endometrial cancer, I'm always thinking about MSI and microsatellite stability. So I was very intrigued by this. We are not seeing a ton of TMB high in our population, but there are some patients that do have that. 

So let's talk a little bit about the results for the collapsed all solid tumor group. What did you find there?

Dr. Herbert Duvivier: In the histology pool cohort, there were 47 patients representing 21 different tumor types, with a median tumor mutational burden of approximately 13 mutations per megabase with a range of 9 to 228. 40 of 47 patients had MSS disease, microsatellite stable disease. 6 of the 47, MSS was not reported, and 1 case was ambiguous. The disease control rate was about 45%, and the objective response rate was 26%. There were 3 complete responses: 1 in bladder, 1 in parotid, and 1 in squamous cell carcinoma. 9 partial responses and 9 stable disease 16 plus weeks. Of interest in the patients that were responding, 10 out of the 21 patients had POLE or POLD1 mutations, and 9 of the 21 patients had BRCA1 or BRCA2 mutations, although most of those mutations were classified as variants of uncertain significance.

Shannon Westin: That's really interesting. We've seen pretty good data for POLE and benefit from immunotherapy, although at least in the GYN tumors and especially in endometrial cancer, those patients usually do well no matter what you do with them. And so they don't often make it to get immunotherapy because they have a complete response up front to their surgeries. So very intriguing to see that driving benefit. I'm just interested to see because it seems like there's a range that you were quoting of what was considered to be TMB high. So did you see a correlation for response to therapy based on how high the tumor mutational burden was in a given tumor or tumor type?

Dr. Herbert Duvivier: Yes, actually we did see a moderately negative correlation between maximum percent change from baseline in a tumor and increasing TMB, which indicated an association between a higher TMB and greater shrinkage of tumor lesions.

Dr. Richard Schilsky: I should point out, by the way, that when we introduced this arm into the TAPUR study, this high tumor mutation burden arm, as Dr. Duvivier has already pointed out, it was prior to, of course, the FDA approval, and the FDA approval is for tumors that have at least 10 mutations per megabase. It was also prior to the adoption of that threshold of 10, based on work by Friends of Cancer Research and others as sort of the convention for what defined a high tumor mutation burden. So when we put this into TAPUR, we essentially consulted with some of the testing laboratories. We consulted with Merck, the sponsor for pembrolizumab and actually in the TAPUR study, we defined a threshold of 9 mutations per megabase as defining high tumor mutation burden. 

Now, as Dr. Duvivier said, there's a broad range of tumor mutation burden represented in this population, and there does seem, if you look at, if the readers want to look at figure 4 in our paper, there does seem to be a general correlation between best response and number of mutations per megabase, which also holds true in a modest way for both progression-free and overall survival. So, TMB is somewhat predictive of favorable outcomes. It's not a perfect biomarker by any means, but generally speaking, if you have enough patients, you can define this sort of trend to support the notion that the more mutations, the greater the likelihood of benefit.

Shannon Westin: That makes a lot of sense. One other thing that I just wanted to comment on before we kind of bring the podcast to a close is I was really struck by the high proportion of underrepresented minorities in this arm of TAPUR, and I just would love to hear your thoughts on how the design improves recruiting in this population of patients.

Dr. Richard Schilsky: This was a goal of the study, very intentional. When you look at the overall study demographics, there are about 2800 patients now that have been enrolled on TAPUR overall. Almost 12% are black, about 6% are Hispanic, about 4% Asian. The median age is about 64. So it's a slightly older population. The goal always was to enroll a population of patients in TAPUR that was broadly representative of the patients that oncologists treat in practice. In the way we accomplished what we've accomplished, we still have work we can do to improve it. But the clinical sites were carefully selected and vetted. We focused on sites that served a significant fraction of minority patients. We made the eligibility criteria simple and broad, so many of the eligibility criteria that might typically exclude minority populations or older patients from clinical trials are not exclusion criteria in TAPUR. We made the operations of the trial simple, so patients really aren't asked to do much more than what they would normally be asked to do in the course of their routine cancer care. So I think all of those things together have made it possible to attract and enroll a more representative patient population in the study. And we're very gratified by that because when you look at many of the registration trials for many cancer drugs, minorities and older people are terribly underrepresented. So we feel that TAPUR is adding value there and adding useful information.

Shannon Westin: I think it's so generalizable and really the way people are practicing, and so to see similar results or concordant results, despite not as much of the rigorous testing and potentially exclusion of certain patient populations is really reassuring and certainly very exciting. 

The last question is what's coming next? What other arms are coming soon? And can sites still join? Is this something where it's ongoing enrollment and participation?

Dr. Richard Schilsky: So sites can still join. There's a place on the ASCO website where sites can find more information about TAPUR, and there's essentially a form available where sites can indicate their interest in joining the study. And then those sites are then evaluated by the TAPUR study team to determine if they meet the minimum necessary requirements to qualify to join the study. There's a lot more data coming out, many more papers that are in press and being written. There are two abstracts that will be presented in April at the AACR meeting. There are three abstracts that have been submitted for the ASCO annual meeting. So a lot more data to come. 

This is a study that, at least hypothetically, could continue in perpetuity as long as we're able to continue to attract new drugs and new treatment combinations onto the TAPUR study platform. So the TAPUR team is always on the lookout for drugs that are about to get an FDA approval and that could be appropriate for the TAPUR study and continue to talk to many pharmaceutical companies about their interest in potentially putting their drugs on the platform.

Shannon Westin: Well, great. Thank you both for taking the time. I know you're both incredibly busy. 

Again, this has been “Pembrolizumab in Patients With Tumors With High Tumor Mutational Burden: Results From the Targeted Agent and Profiling Utilization Registry Study.” I'm your host, Shannon Westin, and I'm so grateful that you joined us on JCO After Hours. Please check out our other offerings on the website or wherever you get your podcasts. Have an awesome day. 

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.

Duvivier's COIs: Speakers' Bureau Company name: Guardant Health Company name: AstraZeneca Company name: Regeneron 

Schilsky's COIs:

Leadership Company name: Clarified Precision Medicine Company name: Leap Therapeutics Stock and Other Ownership Interests Company name: EQRx Company name: Leap Therapeutics Consulting or Advisory Role Company name: Cellworks Company name: Scandion Oncology Company name: Bryologyx Company name: Illumina Company name: EQRx Company name: Syapse Company name: Zephyr AI Company name: AADi Research Funding Company name: AstraZeneca Company name: Bayer Company name: Bristol-Myers Squibb Company name: Genentech/Roche Company name: Lilly Company name: Merck