Invited discussant Susan Slovin, MD, PhD, of Memorial Sloan Kettering Cancer Center, New York, pointed out there are no relevant serum biomarkers for disease progression and the challenges of interpreting response in metastatic castration-resistant prostate cancer. “We should have more definitive criteria and biomarkers that allow us to report PSMA PET [prostate-specific membrane antigen positron-emission tomography] responses in a more consistent manner,” she stated.

“We are trying to look at differences in response with the mean SUV [standardized uptake value]. How do you capture response if there is a greater response in one lesion than another? We are learning how to classify the interpretation of PET ligands. Not every lesion in prostate cancer is PSMA-avid. Patients can have low or minimal PSMA expression,” she said.

“In Dr. Hofman’s abstract, the most interesting finding is that at the 20-month mark, there is no difference in overall survival in the intent-to-treat population. It is still difficult to choose [a treatment at disease progression] among a sea of life-prolonging therapies. For LuPSMA [lutetium-177–labeled PSMA-617], we have only 3 years of follow-up. Many questions remain, including the benefit of radiographic progression-free survival vs overall survival and what clinical state is advised for treatment [with LuPSMA]-minimal disease vs multiple disease sites.” 

DISCLOSURE: Dr. Slovin has served as a consultant or advisor to Bayer, Clovis Oncology, and Pfizer; has served on a speakers bureau for OncLive, PER, Prime Oncology, and the Society for Immunotherapy of Cancer; and has received research funding from AstraZeneca.