Emerging questions with PSMA-PET imaging in prostate cancer

During an educational session during the 2021 LUGPA Annual Meeting, Steven Rowe, MD, PhD, discussed the paradigm-shifting emergence of PSMA-PET imaging in prostate cancer.¹

In an exchange following his presentation, Rowe, an associate professor of Radiology and Radiological Science at Johns Hopkins Medicine addressed key emerging topics in PSMA-PET imaging through a Q&A with session discussants Gordon Brown, DO, FACOS, director of New Jersey Urology’s Center for Advanced Therapeutics, Benjamin Lowentritt, MD, director, Minimally Invasive Surgery and Robotics, Chesapeake Urology.

Brown: The concept of using imaging as a biomarker is a compelling one, and certainly PSMA-PET imaging seems to be able to exclude patients from certain therapies which wouldn't benefit them. Do you see this technology downstream potentially being utilized as a marker for response in those patients to either intensify or de-intensify therapy in patients with advanced disease?

Rowe: Yeah, I think that's a great application for PSMA-PET and there's probably a few different places that it can help us out and as you alluded to, there's a “dealbreaker” that would sort of exclude patients from what might be futile therapies—in the patient who has a rising PSA after radical prostatectomy, if we see something outside of the solid radiation field, it's unlikely that the solid radiation fields can be of any benefit to that patient, so we have to either change the solid radiation field or perhaps…treat that lesion with SBRT. But I think you're also right in that at the systemic therapy level, we can figure out who might be having an early response to therapy, or who has an early progression to therapy and needs to be shifted to a more appropriate therapy.

Lowentritt: The NCCN came out with this very strong statement that conventional imaging is not a necessary prerequisite for PSMA-PET. But they didn't change any of their other recommendations for when to get imaging. I'm curious, is this going to change—with staging especially—when/how we consider doing things that might be standard for certain groups, like when to do a lymph node dissection? Should we always be doing PSMA-PET imaging before we consider doing that and then maybe not doing the dissections if the imaging is negative?

Rowe: As good as PSMA-PET imaging is, I don't ever foresee it replacing a surgical approach to most staging in patients that are presenting with newly diagnosed disease. I think there's an argument to be made that in any patient that would be considered for systemic staging—probably starting as favorable/intermediate risk—that PSMA may be considered as a great alternative to that, and probably preferred at this point, just because it does have an added sensitivity advantage over what we've been using in the past. We don't necessarily have the definitive data yet, but hopefully, we're sort of already at a point where people are exploring that if you see unilateral nodal involvement…perhaps [you can] spare some of the morbidity on the other side where we don’t see anything. But ultimately, I unfortunately just don't see it happening—[PSMA-PET imaging completely replacing] a good node dissection and surgical staging.

Brown: Is there a lead time bias as it relates to the interpretation of some of these [clinical trial] results [with PSMA-PET imaging] from an outcomes perspective?

Rowe: Yeah, I think that's undoubtedly true and something that will be a challenge in the coming years. We still have a lot of work to do to have PSMA-PET intelligently replace conventional imaging for some of the decision-making that we do. But again, just looking at the numbers, it's undoubtedly a better imaging modality. And so, I think it's incumbent upon us to get it in incorporated into clinical trials as fast as we can.

Reference

1. Rowe, S. Society of Nuclear Medicine and Molecular Imaging: Special Session. PSMA Imaging: Is Conventional Imaging Obsolete? 2021 LUGPA Annual Meeting. November 11-13, 2021; Chicago, IL.