Drs. Rana McKay and Jonathan Rosenberg highlight key advances in genitourinary cancers featured at the 2023 ASCO Annual Meeting, including the THOR study in mUCC, VESPER in muscle-invasive bladder cancer, CONTACT-03 in mRCC, and TALAPRO-2 in mCRPC.

TRANSCRIPT

Dr. Rana McKay: Hello, and welcome to the ASCO Daily News Podcast. I'm Dr. Rana McKay, your guest host for the podcast today. I'm a GU medical oncologist at the Morris Cancer Center at the University of California in San Diego and an associate professor at the University of California in San Diego School of Medicine. Joining me today is Dr. Jonathan Rosenberg, the chief of the Genitourinary Oncology Service at the Memorial Sloan Kettering Cancer Center in New York. We'll be discussing practice-changing studies and other key advances in genitourinary cancers that were featured at the 2023 ASCO Annual Meeting.

You'll find our full disclosures in the transcript of this episode, and disclosures of all guests featured on the ASCO Daily News Podcast are available on our transcripts at asco.org/DNpod.

Jonathan, it's great to have you with us today. How are you?

Dr. Jonathan Rosenberg: I'm doing very well. Thanks so much for hosting today.

Dr. Rana McKay: Oh, of course. It's always fun to step back from ASCO and reflect on all the practice-changing and practice-informing studies that were presented.

Dr. Jonathan Rosenberg: Absolutely.

Dr. Rana McKay: Maybe we can dive right in with LBA4619. This is the much-talked-about THOR study of erdafitinib versus chemotherapy in patients with advanced or metastatic urothelial cancer with select FGFR alterations. What are your key takeaways from this study?

Dr. Jonathan Rosenberg: It is indeed a study we've been waiting for, for quite some time, to see the results in the confirmatory study after the accelerated approval of erdafitinib. This is half of the THOR trial. There were 2 cohorts of patients. One cohort were patients who previously received a checkpoint inhibitor randomized to chemotherapy or erdafitinib, and those data were reported at ASCO this year. The other cohort was randomized against a checkpoint inhibitor in patients who have not received a checkpoint inhibitor, and we'll see those data in a future meeting.

The bottom line for the THOR study is that FGFR3 inhibition improved overall survival compared with chemotherapy, and the chemotherapy in this study was a taxane. The overall survival was 12.1 months for erdafitinib compared to 7.8 months for chemotherapy with a hazard ratio of 0.64. This led to the DMC to stop the study and blind the data and cross people over. There was also a PFS advantage. There really weren't a lot of new toxicity signals seen; the usual suspects in terms of mucositis, hyperphosphatemia, diarrhea, dry mouth, and onycholysis.

And so, what it tells us ultimately is that in a patient who's progressed on a checkpoint inhibitor, we can feel comfortable about using erdafitinib knowing it provides a survival advantage in patients who've been previously treated for advanced urothelial cancer and have an FGFR alteration, either an FGFR2 or 3. And hopefully, we'll see more data in the future from the study, maybe not too long in the future from the other part of the study, comparing it to checkpoint inhibition.

Dr. Rana McKay: That's really exciting. I think it's exciting to see the data about the positivity of erdafitinib versus chemotherapy in this context. Looking at the phase 3 data is going to be really important. Looking at the data in the IO naive context is going to be really important. I feel like this sort of reaffirms what we've been doing in clinical practice. But how do you feel that the study is practice-changing?

Dr. Jonathan Rosenberg: I think it gives us reassurance that for these patients, erdafitinib is an appropriate option. There's no randomized data between erdafitinib and other choices, such as sacituzumab, which is also based on an accelerated approval, or enfortumab, which is based on randomized phase 3 trial. But it gives us level-1 evidence. I do wonder whether the comparison against the checkpoint inhibitor may turn out differently, but we'll see. Those data aren't in evidence. And I do think it was interesting that the majority of patients who were enrolled on the trial were PDL-1 low. We'll see what the comparison to a checkpoint inhibitor is like and whether those patients have similar characteristics.

Dr. Rana McKay: Yeah, you're almost kind of selecting for people that were not primed to respond.

Dr. Jonathan Rosenberg: Exactly.

Dr. Rana McKay: Well, that's really exciting, I think. Moving on to localized bladder cancer, Dr. Pfister presented the results of the VESPER trial. That's LBA4507. I think this study was really important. This was a trial that explored dose-dense MVAC with methotrexate, vinblastine, doxorubicin, and cisplatin or gemcitabine-cisplatin as a perioperative chemotherapy for muscle-invasive bladder cancer. I think there's always been some discussion around these regimens and how they pair up against one another. Can you tell us about these data?

Dr. Jonathan Rosenberg: It's a very interesting study. It was designed back when it was felt that we could not give patients neoadjuvant therapy. And it was designed as either a neoadjuvant or adjuvant approach. Although, in reality, almost everybody who was enrolled in the study got neoadjuvant chemotherapy, which I think speaks to the shift in practice over the last 10 to 15 years towards neoadjuvant rather than adjuvant therapy. It's an interesting trial in that it used a duration of chemotherapy for the MVAC regimen, the dose-dense MVAC regimen that we don't usually use, which is 6 cycles. And functionally, about 40% of patients couldn't make it to 6 cycles and had to stop sooner, versus 4 cycles of q3-week gemcitabine and cisplatin.

And what the data show is that the progression-free survival for the entire intent-to-treat population didn't reach significance. But if you looked at the neoadjuvant population only, there was an improvement in progression-free survival as well as overall survival. So, it's sort of a negative positive trial. Negative for the primary endpoint, but positive for key secondary endpoints. They did a very interesting analysis looking at the number of cycles that patients received regardless of arm, but looking at it by arm. And it's clear from that analysis that the more chemotherapy they got, the better they did.

Although, the flaw in that analysis is that the healthier patients are, the more chemotherapy they're able to tolerate, and therefore that may translate to an improved overall survival irrespective of the amount of chemotherapy. And this was not necessarily a pre-specified analysis. I think some of the statisticians were clutching their chests during the report of this trial, having talked to several afterward. On the other hand, it does say to me that for a fit, younger patient, it is important to consider dose-dense MVAC instead of gemcitabine and cisplatin.

I'll also note, reading the publication from the first part of the trial, that it appears that nobody over 70 was enrolled from everything I could tell. And so, I question the validity of the tolerability of the results for the average 75-year-old that I see in my practice. Although age is not a bright line cut-off for anybody in terms of cancer treatment. But my own experience has been that dose-dense MVAC has been harder to tolerate for a lot of patients in their 70s, whereas I think we should feel quite comfortable giving it to patients in their sixties. And if you ask me how many cycles I would give, I probably wouldn't say 6, for dose-dense MVAC, I would probably say 4.

Dr. Rana McKay: Was there a predilection that there was a more aggressive disease like nodal disease or other things to prompt the 6 versus 4?

Dr. Jonathan Rosenberg: I think that they stopped primarily for toxicity reasons, but it wasn't clear to me that it was a disease-based issue. And for the neoadjuvant therapy, everyone was supposed to be clinically node-negative on entry, so that probably wouldn't have explained it.

Dr. Rana McKay: Very exciting. I know that the data were quite provocative, but I think it's always difficult to interpret these sorts of subgroup of subgroup analyses, and there's a lot of bias in why people may get more versus less. And I think trying to reduce these data to clinical practice is going to be really important, as you've stated.

Dr. Jonathan Rosenberg: Rana, I'd also like to talk about some key advances in renal cell carcinoma that were reported at ASCO. Dr. Choueiri presented data on LBA4500, the CONTACT-03 study, which really was the first study of its kind in solid tumors because it addressed a major question in the kidney cancer field and in other fields: Is there a role for immunotherapy rechallenge after progression on immunotherapy? Specifically, the study looked at the efficacy and safety of atezolizumab plus cabozantinib versus cabozantinib alone after progression with prior immune checkpoint inhibitor therapy in metastatic RCC. I'd like you to tell me what you think of this study and the results and how they may affect our practice.

Dr. Rana McKay: Absolutely. This was a critically important study looking at the role of IO post-progression on IO. It was a large phase 3 trial that enrolled patients with clear cell and non-clear cell patients. It actually allowed patients with papillary RCC, unclassified RCC, to enroll in the study, whereas most of these studies are excluding patients with non-clear cell disease. Patients had to have progressed on an immune checkpoint inhibitor given either as adjuvant first line or second line, given either as a single agent or in combination with one of the other combos, whether a VEGF or IO. And patients were randomized one-to-one to receive the combination of atezolizumab plus cabozantinib versus cabozantinib alone. And the dosing of the cabozantinib here is at 60 milligrams in the combination, which is the standard dosing of cabozantinib monotherapy. And the primary endpoints for the trial included PFS and OS.

And in essence, this trial was a completely negative study. The primary endpoint, which was centrally reviewed, rPFS, was negative. The hazard ratio there was 1.03. Overall survival was also negative with a hazard ratio of 0.94. And when you look at the subgroup analyses, there really wasn't any specific subgroup that seemed to derive any benefit, potentially those that had a prior response to an immune checkpoint inhibitor, but in essence, a negative study.

And I think these data are really informative because the discussion at ASCO was conducted by Dr. David Braun, and he actually had conducted a very highly scientific Twitter poll to help guide how to interpret the data and what people do. And from that, about 30% of individuals that completed the poll were actually layering on IO therapy, and continuing IO therapy after somebody progressed on therapy layering in a TKI while keeping the IO backbone going.

And I think what this study proves is that we really don't have any really robust data to guide doing that at the present time. And what we may end up doing is compromising the efficacy of the oral TKI or dose-compromising the oral TKI to try to maintain an ineffective IO. And so, I think at the present time these data, while negative, were truly practice-informing. There are other studies that are looking at this strategy as well. I think one of the criticisms here is that atezolizumab really has not had a great track record in renal cell carcinoma in every single context where it was tested, either alone or in combination. It has not met its primary endpoint and it's not utilized as a treatment in RCC. So, there's some discussion that could this be the fact that this is a PDL-1 inhibitor and that it's atezolizumab. And additionally, I think the thing to point out for is that in the modern era if we look at the cabozantinib control arm, cabozantinib in the refractory setting had a PFS of 10.8 months, which is pretty impressive for a later line PFS, if you will. So, there is another study currently ongoing called the TiNivo-2 study that's looking at tivozanib plus nivolumab versus tivozanib alone in a similar patient population. That trial is enrolling only clear cell patients that had progressed on prior IO. So, I think we'll have additional data, but very, I think, informative. I think this question comes up in a lot in other tumor sites as well because of the broad use of checkpoint inhibitors across hematologic and solid tumor malignancies.

Dr. Jonathan Rosenberg: I think this was the most informative negative study and the most negative trial I've seen in a while as well. But it did highlight the importance of asking these questions where people assume they know the answer already, and in fact, we often don't, and our assumptions are wrong. So, I thought that was fascinating and very well described.

Staying in the kidneys arena. I'd like to talk to you also about the phase 2 KEYNOTE-B61, that's Abstract 4518. It looked at first-line lenvatinib and pembrolizumab across non-clear cell carcinomas. Tell me what you thought of the trial and what your takeaways were.

Dr. Rana McKay: This is an important study. I think the treatment of non-clear cell RCC has lagged. I guess the advances have lagged behind clear cell RCC, and really robust phase 3 randomized studies in people with non-clear cell histologies are very limited. This was a single-arm phase 2, so I think we need to kind of take that for what it's worth, that enrolled patients who had non-clear cell RCC per investigator that had received no prior systemic therapy. So, this was a frontline study, and patients received pembrolizumab plus lenvatinib until disease progression or toxicity.

The study enrolled a very robust 158 patients, which is pretty impressive for a modern-day non-clear cell cohort. We've seen data from nivo-cabo that had gotten presented previously by Dr. Lee. That study was a single institution, about 40 patients or so if you will. The primary endpoint of this study was objective response rate, and the bulk of the patients that were enrolled were papillary RCC. As you would imagine, around 60% of patients were papillary. It did include around 18% with chromophobe RCC. And when we break things down by IMDC risk category, about 44% of patients were favorable-risk disease. I think the percentage of patients who were favorable is higher than if we were to take an all-comer metastatic RCC patient population.

But the objective response rate was pretty impressive at 49% with this combination. The CR rate was right around 5.7%. So, I think certainly a pretty solid signal of efficacy. But again, this is a single-arm phase 2 study. I think what's also really interesting, and I think we have to take subset analyses with a grain of salt if you will, but there were responses that were seen across all histologies. And the prior nivo-cabo study that I had shared with you had previously done a futility analysis for patients with chromophobe RCC, and that cohort actually closed down. And in this study, the response rate for the chromophobe patients, though it wasn't a lot of patients, 29 patients with chromophobia RCC, was around 27.6%, so I think these data are certainly informative. If you look at the waterfall plot, there were some deep responses that were certainly observed, and the bulk of patients had some degree of tumor shrinkage with very little patients that had primary PD.

Dr. Jonathan Rosenberg: It's really provocative. So, are we getting to a point where we might start thinking about randomized trials in the non-clear cell population to try to establish the best standard of care?

Dr. Rana McKay: Well, I think PAPMET2 is currently enrolling patients. That study is looking at the combination of cabozantinib with atezolizumab versus cabozantinib alone for frontline papillary. PAPMET1, which was led by Dr. Pal, I mean, these studies are really magnanimous because it takes all hands on deck to get these patients enrolled because they're few and far between. So, I definitely think we need to be moving in that direction. And I think we need to be moving away from lumping all non-clear cells into one bucket because I think what we're seeing is that, one, the biology of these tumors is very distinct and unique, and they don't all behave the same to any one given therapy. So, we really need to move away from just lumping all non-clear cells into one bucket and try to actually conduct studies for each specific subtype.

Dr. Jonathan Rosenberg: Understood and agree. Let's switch gears for a second and talk about prostate cancer. Can you talk about the data from Abstract 5004, the TALAPRO-2 study of talazoparib and enzalutamide compared to placebo and enzalutamide as a first-line treatment with metastatic CRPC that have HR homologous recombination repair gene alterations?

Dr. Rana McKay: Absolutely. So the TALAPRO-2 study is one of three studies that have looked at the combination of PARP inhibitors with an ARSI in the frontline mCRPC setting. And this trial randomized patients to talazoparib and enzalutamide versus placebo enzalutamide. And again, this was first-line mCRPC. Patients were allowed to have received prior docetaxel or prior abiraterone in the castration-sensitive setting, and the primary endpoint was overall survival.

At GU ASCO this year, we saw the top-line data from TALAPRO-2 first get presented. And what was actually presented at this meeting was the subset of patients that were HRR-mutated only. They had two cohorts: an all-comer cohort that was previously presented, and then now they're presenting the subset of the patients that were HRR-mutated. And I think what we've seen across the board is that the efficacy of PARP inhibitors kind of differs by underlying HRR mutations.

When we look at the entire population of HRR-deficient patients, the study was positive, talazoparib plus enzalutamide resulted in an improvement in rPFS compared to enzalutamide placebo. The hazard ratio there was 0.45. And then when we break things down by selected gene groups, they did this subset analysis in patients with only BRCA1, only BRCA2, only PALB2, only CDK12, ATM CHEK2 if you will. The data are most robust for those patients with a BRCA1/2 alteration with hazard ratios of 0.17, 0.19. Again, this is for rPFS.

But then, when we look at some of these other mutations, like ATM CHEK2, hazard ratios are higher, 0.76, 0.90. So, the effect size really kind of drops off for those non-BRCA1/2 altered HRR genes. But if we look across the different subgroup analyses, the interim OS data for the HR deficient, the time to PSA, time to cytotoxic chemo, all of that favored the combination versus placebo enzalutamide for patients that were HR deficient if we just lumped everybody all together.

Dr. Jonathan Rosenberg: How does this fit into the general landscape around this question with selection versus not selecting for HRR alterations?

Dr. Rana McKay: The data that were presented were for the selected patients, and I think that that's not where the controversy is. I think that the selected patients are the ones that seem to derive the most benefit. It's interesting because in looking at the data from PROpel and the final FDA label based off of the PROpel data, the label is only for BRCA1 and 2 patients and not for all comer HRR. It's even a more restricted label than olaporib monotherapy. So, I think it's going to be interesting. I don't know what the right answer is. I think it's going to be interesting to see how this is going to unfold for TALAPRO-2 and even for MAGNITUDE, if you will, like, how select is the selected population going to be. But at the present time, I think the label is what it is for olaparib plus abiraterone in those BRCA1/2 frontline. My hope is that this population is shrinking because everybody should be getting escalated in the metastatic hormone-sensitive setting, and we shouldn't be having people who are naive to an ARSI in frontline mCRPC.

Dr. Jonathan Rosenberg: Understood and agreed.

Dr. Rana Mckay: Well, thank you so much, Jonathan, for joining me today. It's really been a pleasure kind of going through all of the compelling advances in GU cancers from ASCO. I think it was a really exciting meeting, and thanks for your time.

Dr. Jonathan Rosenberg: My pleasure. It's been great to talk to you today.

Dr. Rana Mckay: And thank you to our listeners for your time today. You will find links to the abstracts discussed today in the transcript of this episode. Finally, if you value the insights that you hear on the ASCO Daily News Podcast, please take a moment to rate, review, and subscribe wherever you get your podcast.

Disclaimer:

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. Guests' 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.

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Disclosures:

Dr. Rana McKay:

Consulting or Advisory Role: Janssen, Novartis, Tempus, Exelxis, Pfizer, Bristol-Myers Squibb, Astellas Medivation, Dendreon, Bayer, Sanofi, Merck, Vividion, Calithera, AstraZeneca, Myovant, Caris Life Sciences, Sorrento Therapeutics, AVEO, Seattle Genetics, Telix, Eli Lilly, Pfizer, Bayer, Tempus

Dr. Jonathan Rosenberg:

Honoraria: UpToDate, Medscape, Peerview, Research To Practice, Clinical Care Options, Physician Education Resource, MJH Life Sciences, EMD Serono, Pfizer

Consulting or Advisory Role: Lilly, Merck, Roche/Genentech, AstraZeneca/MedImmune, Bristol-Myers Squibb, Bayer, BioClin Therapeutics, QED Therapeutics, Pharmacyclics, GlaxoSmithKline, Janssen Oncology, Astellas Pharma, Boehringer Ingelheim, Pfizer/EMD Serono, Merck Therapeutics, Immunomedics, Tyra Biosciences, Infinity Pharmaceuticals, Gilead Sciences, Hengrui Pharmamedical, Alligator BioScience, Imvax

Research Funding (Institution): Genentech/Roche, Seattle Genetics, Bayer, AstraZeneca, QED Therapeutics, Astellas Pharma

Patents, Royalties, Other Intellectual Property (Institution): Predictor of platinum sensitivity

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