Host Dr. Davide Soldato and guests Dr. David Einstein and Dr. Ravi Madan discuss JCO article, "National Cancer Institute's Working Group on Biochemically Recurrent Prostate Cancer: Clinical Trial Design Considerations," underscoring the need for a consensus on clinical trial designs implementing novel endpoints in this population and the importance of PSA doubling time as a prognostic factor, with an emphasis on treatment de-escalation to limit toxicity and improve patient outcomes. TRANSCRIPT The disclosures for guests on this podcast can be found in the show notes. Davide Soldato: Hello and welcome to JCO After Hours, the podcast where we sit down with authors from some of the latest articles published in the Journal of Clinical Oncology. I am your host, Dr. Davide Soldato, medical oncologist at Ospedale San Martino in Genoa, Italy. Today, we are joined by JCO authors Dr. David Einstein and Dr. Ravi Madan. Dr. Einstein is a medical oncologist specializing in genitourinary malignancy working at Beth Israel Deaconess Medical Center, part of the DFCI Cancer Center, and an assistant professor at Harvard Medical School. Dr. Madan is a senior clinician at the National Cancer Institute (NCI), where he focuses on conducting clinical research in prostate cancer, particularly in the field of immunotherapy. Today, we will be discussing the article titled, "National Cancer Institute's Working Group on Biochemically Recurrent Prostate Cancer: Clinical Trial Design Considerations." So, thank you for speaking with us, Dr. Einstein and Dr. Madan. David Einstein: Thanks for having us. This is a great pleasure. Ravi Madan: Appreciate being here. Davide Soldato: So, I just want to start from a very wide angle. And the main question is why did you feel that there was the need to convey a consensus and a working group to talk about this specific topic: biochemically recurrent prostate cancer? What has been the change in current clinical practice and in the trial design that we are seeing nowadays? And so, why was it necessary to convey such a consensus and provide considerations on novel clinical trials? David Einstein: Yeah, so I think it's very interesting, this disease state of biochemically recurrent prostate cancer. It's very different from other disease states in prostate cancer, and we felt that there was a real need to define those differences in clinical trials. Years ago, metastatic castration-resistant prostate cancer was the primary disease state that was explored, and over time, a lot of things shifted earlier to metastatic disease defined on a CAT scan and bone scan to an earlier disease state of metastatic castration-sensitive prostate cancer. And the clinical trial principles from late-stage could be applied to MCSPC as well. However, BCR is very different because the patients are very different. And for those reasons, there are unique considerations, especially in terms of toxicity and treatment intensity, that should be applied to biochemically recurrent prostate cancer as opposed to just using the principles that are used in other disease states. And for that reason, we thought it was very important to delineate some of these considerations in this paper with a group of experts. Davide Soldato: Thanks so much. So, one of the main changes that have been applied in recent years in clinical practice when looking at biochemically recurrent prostate cancer is the use of molecular imaging and particularly of PSMA PET. So, first of all, just a quick question: was the topic of the consensus related on which threshold of PSA to use to order a PET scan to evaluate this kind of patient? David Einstein: Yeah, thanks for that question. It's a super important one. The brief answer is that no, we did not address questions about exactly when clinicians would decide to order scans. We were more concerned with the results of those scans in how you define different disease states. But I think as a broader question, I think a lot of folks feel that finding things on a scan equates that with what we used to find on conventional scans. And fundamentally, we actually sought to redefine that disease space as something that's not equivalent to metastatic disease, and rather coined the term "PSMA-positive BCR" to indicate that traditional BCR prognostic criteria and factors still apply, and that these patients have a distinct natural history from those with more advanced metastatic disease. Ravi Madan: And if I may just add that the National Cancer Institute is running a trial where we're prospectively monitoring PSMA-positive BCR patients. And that data is clearly showing that, much like what we knew about BCR a decade ago, PSMA findings in BCR patients do not change the fact that overall, BCR is an indolent disease state. And the findings, which are usually comprised of five- to seven-millimeter lymph nodes, do not endanger patients or require immediate therapy. And so, while PSMA is a tool that we can be using in this disease state, it doesn't really change the principal approach to how we should manage these patients. And as Dr. Einstein alluded to, there is a drive to create a false equivalency between PSMA-positive BCR and metastatic castration-sensitive prostate cancer, but that is not supported by the data we're accumulating or any of the clinical data as it exists. Davide Soldato: One thing that it's very important and you mentioned in your answer to my question was actually the role of PET scan and conventional imaging, so CAT scan and bone scan that we have used for years to stage patients with metastatic prostate cancer. And you mentioned that there is a distinction among patients who have a positive PET scan and a BCR, and patients who have a positive conventional imaging. And yet, we know that sometimes the findings of the PET scan are not always so clear to interpret. So, I just wanted to understand if the consensus reached an agreement as to when to use conventional imaging to potentially resolve some findings that we have on PET scan among thess patients with BCR? David Einstein: Yeah, I think there's a number of questions actually buried within that question. One of which is: does PSMA PET result in false positives? And the answer has definitely been yes. There's a known issue with false-positive rib lesions. And so, first and foremost, we need to be very careful in calling what truly is suspicious disease and what might actually not be cancer or might be something that is totally separate. So I think that's the first part of the answer to that question. The second is to what extent do we need to use paired PET and conventional imaging to define this disease state? In other words, do you have to have positive findings on one and negative findings on the other in order to enter this definition? The challenge there, as we discussed, is that logistically, oftentimes it's hard to get patients to do multiple sets of scans to actually create that definition. Sometimes it's difficult to get insurers to pay for such scans. And finally, it's hard to sometimes blind radiologists to the results of one scan in reading the other. So, we did have some deliberations about to what extent you could use some of the CAT scan portion of a PSMA PET in order to at least partially define that. We also talked about using bone scans to confirm any bone findings seen on PET. But I think another important part of this is not just the baseline imaging, but also what's going to be done serially on a study in order to define responses and progression. And that's sort of a whole separate conversation about to what extent you can interpret changes in serial PET. Ravi Madan: And just to pick up on the key factor here, I think that the PSMA PET in BCR is pretty good at defining lymph node disease, and that's actually predominantly 80 to 90 percent of the disease seen on these findings. It might be pretty good at also defining other soft tissue findings. The real issues come to bone findings. And one thing the group did not feel was appropriate was to just define only PSMA-positive bone findings confirmed on a CT bone window. There's not really great data on that, but the working group felt that, when in the rare situation, because it is relatively rare, a PSMA-positive finding is in a bone, a bone scan should be done. And it's worth noting that Phu Tran, who is a co-author and a co-leader of this working group, his group has already defined that underlying genomics of conventionally based lesions, such as bone scan, are more aggressive than findings on next-gen imaging, such as PSMA. So, there is also a genomic underlying rationale for defining the difference between what is seen on a PET scan in a bone and what is seen on a bone scan. Davide Soldato: Coming back to this issue of PET PSMA sometimes identifying very small lesions where we don't see any kind of correlates on conventional imaging or where we see only very little alteration on the bone scan or in the CT scan, was there any role that was imagined, for example, for MRI to distinguish this type of findings on the PET scan? Ravi Madan: So, I think that, again, what can be identified on a PSMA frequently cannot be seen on conventional imaging. We didn't feel that it was a requirement to get an MRI or a CT to necessarily confirm the PSMA findings. I think that generally, we have to realize that in this disease state, that questionable lesions are going to be seen on any imaging, including PSMA. We've actually probably put way too much faith in PSMA findings thus far, as Dr. Einstein alluded to with some of the false positives we're seeing. So, I think that these false positives are going to have to be baked into trials. And in terms of clinical practice, it highlights the need to again, not overreact to everything we see and not necessarily need to biopsy everything and put patients' health in jeopardy to delineate a disease that's indolent anyw