Parp Anibitar Rookaparib - The Primary Results From the Triton 3 Trial

Guest host Dr. Neeraj Agarwal and Dr. Christian Kollmannsberger discuss practice-changing abstracts that were presented at the 2023 ASCO Genitourinary Cancers Symposium, including results from the TALAPRO-2, PROpel, TRITON3, ARASENS, KEYNOTE-057, CheckMate 274, and CheckMate 9ER studies.

TRANSCRIPT

Dr. Neeraj Agarwal: Hello and welcome to the ASCO Daily News Podcast. I'm Dr. Neeraj Agarwal, the director of the Genitourinary Oncology Program, and professor of Medicine at the Huntsman Cancer Institute at the University of Utah, and editor-in-chief of the ASCO Daily News.

Today, we will be discussing practice-changing abstracts and other key advances in GU Oncology featured at the 2023 ASCO Genitourinary Cancers Symposium. Joining me for this discussion is Dr. Christian Kollmannsberger, the chair of this year's ASCO GU. Dr. Kollmannsberger is a GU medical oncologist at the BC Cancer Vancouver Cancer Center and a clinical professor at the University of British Columbia.

Our full disclosures are available in the transcript of this episode, and the disclosures of all guests on the podcast can be found on our transcripts at asco.org/DNpod.

Christian, thank you for joining us on the podcast today.

Dr. Christian Kollmannsberger: Thank you very much, Neeraj. It's a real pleasure to be here and have this discussion.

Dr. Neeraj Agarwal: Thank you. So, Christian, the GU meeting featured remarkable progress in various GU malignancies. Could you please share some of the prominent topics that made the headlines this year and give us an overall feel of ASCO GU this year?

Dr. Christian Kollmannsberger: Absolutely. I think it was a great meeting with over 5,800 attendees from more than 70 countries. And most of the attendees were in person, so it was a great event. ASCO GU is truly the premier global event to feature the very best of GU cancer research and treatment. The theme of this year's meeting was "Today's Science, Tomorrow's Treatment," and that was reflected in the novel scientific and clinical findings that were presented and will potentially lead to changes in our daily clinical practice. It also reminds us how quickly the development today is and how quickly novel scientific progress is immediately translated into clinical practice, particularly oncology.

I was very impressed by the meeting's emphasis on diversity, interactivity, networking, multidisciplinary collaboration, and evidence-based care. We introduced several new features such as a "Meet the Professor session, a women's networking event, etc. And the first day really kicked off with a very rich focus on prostate cancer and much attention given to PARP inhibitors in our first session. As an example, LBA 17 was the first late-breaking abstract presented. And congratulations to you, Neeraj, on delivering this exciting data on the TALAPRO-2 trial, which were eagerly awaited. Let's start with that. Can you tell us about this trial?

Dr. Neeraj Agarwal: Yes, of course. So the TALAPRO-2 trial was a phase 3 randomized trial where patients in newly diagnosed metastatic CRPC settings were randomized to standard of care enzalutamide plus placebo versus enzalutamide plus talazoparib PARP inhibitor. And as we know, Christian, the rationale has been that dual inhibition of PARP and AR may enhance the efficacy of each. And there's a laboratory preclinical rationale and based on which other studies have been done in the past. So, without getting into too much detail into the rationale for the trial, I'll come right to the results of the trial. So, this was the first-line mCRPC setting where rPFS was the primary endpoint as assessed by the independent radiology assessment. And in this trial, patients were recruited regardless of the homologous recombination repair gene alterations. So, patients were recruited and they were prospectively tested for whether they had these HRR gene alterations or not, but all comer population was included in this trial. And after a median follow-up of approximately 23 months, the trial read out, and we found that trial made the primary endpoint was improved radiographic progression-free survival with the rPFS being about 22 months in the enzalutamide arm and not reached in the combination arm with a 37% reduction in risk of progression or death.

If you look at the subgroup analysis of patients who were HRR+, there was a 54% reduction risk of progression or death. If you look at patients who were stratified in HRR- or unknown group, there was a 30% reduction risk of progression or death. If you specifically look at an exploratory analysis we did to look for patients who were HRR- by prospective tumor tissue testing; there was a 34% reduction in risk of death with a hazard ratio of 0.66 favoring the combination arm. So overall, the rPFS primary endpoint was met in all groups. We also see significant delay in PSA progression in the combination arm by more than nine months. We also see delays in the time to cytotoxic chemotherapy. We saw delay in progression or death on subsequent neoplastic therapy after the protocol treatment. We saw delays in deterioration of quality of life and global health status. All these were significant and happened on the talazoparib plus enzalutamide arm.

So overall, if you look at the totality of the data, these all favored the combination of talazoparib plus enzalutamide compared to enzalutamide alone. I want to highlight that overall survival is immature at 31% maturity with a hazard issue of 0.89, currently favoring enzalutamide plus talazoparib. But we'll have to look at more mature data as time passes.

Dr. Christian Kollmannsberger: Wow. Thank you, Neeraj. So, it sounds like that was a very positive trial, and it's potentially practice-changing. One of the concerns is always safety and toxicity. So can you tell us whether there were any new safety signals, and can you tell us more about the common adverse events that were noticed in TALAPRO-2?

Dr. Neeraj Agarwal: No discussion is complete without talking about safety results, so I'm glad you asked me, Christian. The most common dose-affecting toxicity, if you will - so toxicities which led to dose modification and dose discontinuation of talazoparib were cytopenias, as we expect from this class of agents. So anemia, neutropenia, thrombocytopenia, these were the common toxicities. In fact, rate with anemia was 46.5%. Neutropenia and cytopenia were much less common.

I would like to highlight one fact which also came up during the discussion section after our oral presentation. The qualifying criteria for entry in this trial was a hemoglobin of 9-gram percent. And 49% of patients had grade 1 to 2 anemia at baseline, that is before starting treatment with talazoparib. So, we knew that if you mandate dose reduction, a lot of patients will not get adequate dosing of talazoparib. So, we waited for grade 3 anemia and then instituted dose reduction. And that I thought personally was a good strategy because the grade 3 anemia happened after a median duration of three months, 3.3 months to be more precise. And then, these patients underwent protocol-mandated dose reduction, following which the dose discontinuations were quite low actually. Only 8.3% patients discontinued talazoparib because of anemia, and the median dose intensity or median relative dose intensity of talazoparib in the talazoparib arm remained quite high at more than 80%, which translates to a talazoparib dose of 0.4 milligram daily when the starting dose was 0.5 milligram. So those were the hallmark of toxicities.

I do like to mention that those grade 3, 4 toxicities which are more known to affect the quality of life of our patients, such as grade 3, 4 anorexia, fatigue, nausea and vomiting, they were quite rare, happening in 1 to 4% patients who were on talazoparib. So overall, regarding the side effects, they were manageable, there were no new safety signals, and we could maintain adequate talazoparib dosing with dose reduction, which happened quite early during the protocol treatment.

Dr. Christian Kollmannsberger: Thank you, Neeraj. Very impressive results indeed. The patient population included in TALAPRO-2 was very similar to those included in the PROpel phase 3 trial, which tested the combination of abiraterone and olaparib in the first-line mCRPC setting. So, I'd like to just mention that we also saw LBA16 on the PROpel study, which was the final overall survival in PROpel, which was presented by Noel Clarke. So PROpel, as you know, was a randomized phase 3 trial evaluating efficacy and safety of olaparib plus abiraterone versus placebo plus abiraterone as first-line therapy for mCRPC in the first-line metastatic castration resistance setting. The enrollment in that study was independent of known defects in the homologous recombination repair gene pathway in contrast to other studies, such as MAGNITUDE, which tested the biomarker upfront. A total of 796 patients were randomly assigned to either olaparib plus abiraterone or placebo plus abiraterone. And we saw similar results, significant radiographic progression-free survival with olaparib plus abiraterone in PROpel, which was the primary endpoint similar to TALAPRO-2, and that was published last year in the New England Journal of Medicine Evidence.

Now, this abstract presented here at ASCO GU reported on overall survival with an overall survival majority of 47.9% and showed that with the addition of the PARP inhibitor olaparib to abiraterone, a statistically non-significant but clinically meaningful improvement in overall survival of about seven months were achieved compared to standard of care in abiraterone alone. The numbers were 42.1 versus 34.7 months in the all-comers population of patients in the first-line mCRPC setting. Importantly, I think the median overall survival of more than 42 months really represents the longest reported median overall survival thus far in a phase III trial for first-line metastatic castration-resistant prostate cancer. Although the median overall survival for the non-HRR group remains not statistically significant, with a hazard ratio of 0.89.

Dr. Neeraj Agarwal: Such a great synopsis of the PROpel result data. Thank you, Christian, for highlighting these results. As we know, the combination is already approved by the EMA, the European Medical Agency, for patients in the first-line mCRPC setting who are not candidates for docetaxel chemotherapy. If this combination is approved by the FDA, we may have one more therapeutic option for our patients in first-line mCRPC.

So, just continuing on the PARP inhibitors, there was one more oral presentation with PARP inhibitor rucaparib by Dr. Alan Bryce from the Mayo Clinic, Arizona. This was Abstract 18 on the primary result of the TRITON3 trial. So to complete our PARP inhibitor section, I would like to summarize the result of the TRITON3 trial, which was a randomized phase III trial evaluating rucaparib versus physician choice, which notably included docetaxel in addition to abiraterone or enzalutamide in patients with chemotherapy-naive mCRPC with BRCA1, BRCA2 or ATM alterations. These patients had disease progression after having one novel hormonal therapy, or we call them second-generation androgen pathway inhibitors in any setting. So these patients had to have disease progression on a novel hormonal therapy.

In the BRCA subgroup and the subsequent intention to treat the population, the primary endpoint tested first was radiographic progression-free survival, and overall survival was the key secondary endpoint. The subgroup of patients with BRCA-altered disease had a median rPFS of 11.2 months with rucaparib compared to 6.4 months with physician choice of treatment - looks like almost doubling of the rPFS with the rucaparib. In the overall ITT population, median rPFS was 10.2 months with rucaparib and 6.4 months with the physician's choice of treatment. Although the overall survival data are immature, we still see a trend for improved overall survival with rucaparib. Regardless, the study clearly demonstrates the value of rucaparib for treating BRCA1 and BRCA2-altered mCRPC after disease progression on an androgen receptor pathway inhibitor. So these were the impressive results from the TRITON3 trial.

But before we switch to non-prostate abstract, I would like to complete the prostate cancer discussion by talking about the Abstract 15, which was based on the results of the ARASENS trial presented by Dr. Maha Hussain. As we know, ARASENS is a randomized phase 3 trial evaluating the efficacy and safety of darolutamide plus androgen deprivation therapy plus docetaxel versus androgen deprivation therapy or ADT plus docetaxel. So the triplet of ADT plus darolutamide plus docetaxel being compared to ADT plus docetaxel chemotherapy in patients with newly diagnosed metastatic castration-sensitive prostate cancer. A total of 1,300 patients were randomly assigned to the doublet versus triplet. As presented in the last ASCO GU meeting exactly one year ago, the primary endpoint of the study was met with a significant improvement in overall survival and a 32% reduction in risk of death for patients on the triplet therapy with ADT plus docetaxel plus darolutamide versus ADT plus docetaxel chemotherapy. So triplet therapy was already approved based on these data.

The abstract presented by Dr. Hussain this year is a post-talk analysis where Dr. Hussain and colleagues investigated the impact of triplet therapy across patients with high volume versus low volume per chartered criteria and higher risk versus low risk using latitude trial criteria. And investigators knew that these results would be highly attractive to practicing oncologists who are now choosing treatment based on volume of disease or risk of disease, more commonly, volume of disease.

So, let's come to what was presented this ASCO GU. So, after 1,305 patients in ARASENS, the majority had high-volume disease and high-risk disease. Among patients with high-volume disease, the addition of darolutamide reduced the risk of death by 30% compared with ADT and docetaxel, with a hazard ratio of 0.69. In the risk groups, the addition of darolutamide seems to favor both high-risk and low-risk groups. Among patients with low-volume disease, there was a trend towards improvement in overall survival with the addition of darolutamide, but it did not reach statistical significance. The great news was that there was no new safety signal. So, to summarize these data, the triplet of darolutamide plus ADT plus docetaxel showed superior overall survival compared to doublet of ADT plus docetaxel, with an important caveat that triplet was not compared with any of the modern doublets of ADT plus a second generation androgen receptor pathways inhibitor such as abiraterone, apalutamide, or enzalutamide, or even darolutamide. So, I wish there was a third arm of ADT plus darolutamide.

Having said that, triplet can be considered a standard of care now based on these data for patients with metastatic hormone sensory prostate cancer, where we would be using ADT plus docetaxel chemotherapy. And from this meeting data, this efficacy of triplet can be applied to high-volume disease and all risk disease. And we just need more time to see how the data pans out in low-volume patients with metastatic hormone-sensitive prostate cancer.

Dr. Christian Kollmannsberger: Yes, I completely agree, Neeraj. I think all the data presented in these abstracts are really impressive and will impact our daily clinical practice and our patients more or less immediately. I think the use of PARP inhibitors, whether as a monotherapy or in combination with androgen receptor pathway inhibitors, as well as now the option of triplet therapy in the metastatic castration sensitive setting really offer patients with metastatic prostate cancer new treatment strategies and most importantly, improved survival outcomes. And it is impressive to see how we have pushed the prognosis and the outcomes for our patients with prostate cancer, I would say, in the last five to ten years. And similar to last year, I think the entire Prostate Cancer Day at ASCO GU 2023 was full with impressive data and featured dynamic content throughout the day.

Dr. Neeraj Agarwal: Indeed. So, let's move on to bladder cancer. Christian, what are your key takeaways from the bladder cancer studies presented at the meeting?

Dr. Christian Kollmannsberger: I think there were interesting abstracts in both the non-muscle-invasive and the muscle-invasive setting and the metastatic setting. So, for example, Abstract 442 was presented by Dr. Andrea Necchi on the cohort B of the phase 2 KEYNOTE-057 trial. As a background here, the standard treatment for high-risk non-muscle-invasive bladder cancer involves transurethral resection of the bladder tumor, a TURBT, followed by intravesical BCG therapy to eradicate any residual disease. And patients who fail to adequately respond to BCG are usually recommended to undergo radical cystectomy. So in the cohort B of the phase 2 KEYNOTE-057 trial that investigated the safety and efficacy of pembrolizumab as a single agent for patients with BCG-unresponsive, high-risk non-muscle-invasive bladder cancer who were ineligible or declined to undergo radical cystectomy, enrolled patients received standard-dose pembrolizumab of 200 milligrams every three weeks for up to 35 cycles. So very common as we do it with other disease sites. And at a median follow-up of 45.4 months, the primary endpoints of disease-free survival at twelve months was 43.5%. The median disease-free survival duration was 7.7 months. These are encouraging results, and we should keep in mind that a radical cystectomy has immense impact on our patients' quality of life. So I think it is important that we do these trials.

Now in order to address potential biases in this phase II trial, such as the underlying heterogeneity of transurethral resection of bladder tumor quality, and to obtain a more comprehensive understanding of pembrolizumab's efficacy relative to a particular control group, we need further evaluation of pembrolizumab in a randomized trial before we can really go for regulatory approval. But overall, I think for the first time in a long time that we seem to be able to move the needle in non-muscle-invasive bladder cancer.

Dr. Neeraj Agarwal: Thank you, Christian, for this great overview. Could you please also share the findings presented by Dr. Matt Galsky on Abstract 443?

Dr. Christian Kollmannsberger: Of course, Neeraj. Abstract 443, presented by Matt Galsky, reported the extended follow-up results from the CheckMate 274 trial, which looked at another very important field where we haven't made that much progress, which is the adjuvant setting. And CheckMate 274 examined adjuvant nivolumab compared to placebo for patients with high-risk resected muscle-invasive urothelial carcinoma. In this trial, nivolumab was given at 240 milligrams every two weeks or placebo every two weeks for up to one year of treatment. After following up with patients for a median of 36.1 months, the study found that those who received nivolumab had a median DFS of 22 months compared to only 10.9 months for those who received placebo among the ITT patients. So basically, a doubling of the DFS with the addition of adjuvant nivolumab.

The results were particularly notable for patients with high PD-L1 expressions or PD-L1 expression of 1% or more, as those who are treated with nivolumab had a median DFS of 52.6 months, which was six times higher than the DFS in the control group where patients received placebo, which was only 8.4 months. And I think that is truly impressive. One year of adjuvant therapy with nivolumab continues to show a sustained disease-free survival benefit over a period of three years in both the ITT and the PD-L1-high patient population. In my view, these results reinforce the utility of nivolumab in the adjuvant urothelial carcinoma setting after surgery. And it will be interesting to see how the overall survival pans out in this study.

So, Neeraj, moving on to kidney cancer, what were your key takeaways from these studies on kidney cancer presented in this meeting?

Dr. Neeraj Agarwal: So, there were exciting results presented from multiple studies in this area as well. For example, Abstract 603 presented by Dr. Mauricio Burotto, senior author was, Dr. Toni Choueiri on the three-year follow-up from the phase 2 CheckMate-9ER trial. So, in this trial, patients were randomized one-to-one to nivolumab 240 milligrams every two weeks, plus cabozantinib 40 milligrams daily versus sunitinib 50 milligrams daily for four weeks, and it was a six-week cycle for sunitinib until disease progression or unacceptable toxicity. So this was the design of the phase 3 CheckMate-9ER trial. And after a median follow-up of three years, the benefit of nivolumab plus cabozantinib remained consistent with previous follow-ups. So, as we know, these data have been presented in the past, also published in the New England Journal of Medicine. But this meeting was a clear follow-up of these data.

Notably, the median overall survival of patients treated with cabozantinib plus nivolumab in the ITT population, which included all favorable intermediate and poor IMDC score patients, was significantly improved at 49.5 months compared to 35.5 months in the sunitinib arm. It is so heartening to see that median overall survival breaching the four-year mark in our patients with metastatic RCC in a consistent fashion. We saw similar data with the combination of ipilimumab plus nivolumab recently. And as these trials are maturing, we are probably going to see more combinations breaching this four-year mark. So importantly, no new safety signals emerged with the additional follow-up in either arm. And I think these results provide further support for the use of cabozantinib plus nivolumab as a first-line treatment option for patients with metastatic or advanced renal cell carcinoma.

Dr. Christian Kollmannsberger: Indeed, I think it is extremely impressive what we've seen over the last 15 years in metastatic kidney cancer, going from a median overall survival of about a year to now more than four years. I think that is a great achievement, and we can see it on a daily basis in our clinical practice.

Now, before we wrap up, I would like to highlight another potentially practice-changing trial, LBA602, which titled, "Results from Phase 3 Study of 89Zr-DFO-Girentuximab for PET/CT Imaging of Clear Cell Renal Cell Carcinoma: The ZIRCON Trial" presented by Dr. Brian Shuch. The background of this is that the detection of renal masses poses a challenge due to the limitations of diagnostic options such as imaging and biopsy. And we often, in clinical practice, are confronted with "What exactly is this?" And what's even more importantly, "What's the histology of this?" And a non-invasive, accurate method is needed for pre-treatment risk stratification. Girentuximab, a monoclonal antibody that targets carbonic anhydrase IX expressed on clear cell renal cell carcinoma, can obviously now aid in the differentiation between clear cell renal cell carcinomas and other renal lesions when radiolabeled with this new agent.

The ZIRCON trial was open-label and designed to include patients with renal masses up to 7 cm in size or clear tumor stage cT1 who were scheduled for partial nephrectomy within 90 days of planned TLX250-CDx administration. The enrolled patients received a single intravenous dose of girentuximab on day 0 and underwent FDG PET/CT imaging on day 5 before their scheduled surgery. And the co-primary endpoints were to assess the sensitivity and specificity of girentuximab PET/CT imaging for detecting clear cell renal cell carcinoma in patients with indeterminate renal masses, with histology as the reference standard, which I think is a great way to test these agents because you get 100% validation.

In the primary analysis of 284 patients, the average sensitivity and specificity across all three central readers were 86% and 87%, respectively, exceeding the prespecified thresholds. The positive and negative predictive values were 93.4% and 78%, respectively. And with very few related adverse events reported, the study affirms that girentuximab PET/CT is safe and effective in identifying clear cell renal cell carcinoma in patients with indeterminate renal masses. And the findings hold potential for developing optimal management strategies for patients with indeterminate renal masses. I think this is important that we add a non-invasive method to this because we are confronted on a regular basis with patients who either cannot tolerate a biopsy or where the biopsy is indeterminate. And this could potentially be a great tool to help us with our pre-treatment planning of our treatment strategy.

Dr. Neeraj Agarwal: Wow. So, it looks like a new PET scan using a unique tracer and antibody to detect the clear cell renal cell carcinoma with high specificity and sensitivity. It reminds me of drawing a crude analogy from the PSMA PET scan in prostate cancer. And hopefully, we will be able to use these newer scans that we call TLX250-CDx PET/CT scan. I hope they have a simpler name for this very soon. Or maybe follow up for patients who had kidney cancer, localized kidney cancer taken out by radical surgery, and then we are following them. And sometimes, we don't know if a small lung nodule is metastatic or not. And these kinds of imaging studies may help us down the line in monitoring those patients as well. So indeed, very exciting progress not only in the therapeutic area now but also in diagnostic fields at this GU ASCO.

So with that, we have seen multiple abstracts on prostate, bladder, and kidney cancer with real impact on how we practice medicine. Thank you, Christian, for sharing your insight with us today. It is an exciting time in GU Oncology, and we appreciate you taking the time to contribute to the discussion. Thank you so much.

Dr. Christian Kollmannsberger: Thank you, Neeraj, thank you for having me. And I completely agree it remains an exciting time in GU oncology.

Dr. Neeraj Agarwal: And thank you to our listeners for joining us today. You will find links to the abstracts discussed today on the transcripts 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 podcasts.

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. 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.

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Dr. Neeraj Agarwal

@neerajaiims

Dr. Christian Kollmannsberger

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Disclosures:

Dr. Neeraj Agarwal:

Consulting or Advisory Role: Pfizer, Bristol-Myers Squibb, AstraZeneca, Nektar, Lilly, Bayer, Pharmacyclics, Foundation Medicine, Astellas Pharma, Lilly, Exelixis, AstraZeneca, Pfizer, Merck, Novartis, Eisai, Seattle Genetics, EMD Serono, Janssen Oncology, AVEO, Calithera Biosciences, MEI Pharma, Genentech, Astellas Pharma, Foundation Medicine, and Gilead Sciences

Research Funding (Institution): Bayer, Bristol-Myers Squibb, Takeda, Pfizer, Exelixis, Amgen, AstraZeneca, Calithera Biosciences, Celldex, Eisai, Genentech, Immunomedics, Janssen, Merck, Lilly, Nektar, ORIC Pharmaceuticals, crispr therapeutics, Arvinas

Dr. Christian Kollmannsberger:

None disclosed