Prospective monitoring of prostate specific membrane antigen–positive biochemically recurrent prostate cancer (PSMA+ BCR): Preliminary data from 6-month PSMA follow-up.

5098 Background: PSMA imaging can identify recurrent prostate cancer after definitive surgery/radiation prior to detection on computed tomography (CT) or bone scan. Radiation to PSMA+ findings is common but lacks clear data demonstrating long term benefit. PSMA+ biochemically recurrent prostate cancer (PSMA+ BCR) is often defined and treated as metastatic castration sensitive prostate cancer (mCSPC), yet PSMA imaging alone as an eligibility criteria was never studied in the mCSPC trials. PSA+ BCR requires better understanding to define at-risk patients (pts). Methods: NCT05588128 enrolls pts after definitive and possibly salvage therapies. Pts are required to be 1 year removed from definitive therapy with a PSA>0.5 ng/ml, testosterone>100 ng/dL, and negative CT/bone scans. Lymph nodes (LNs) up to 1.5 cm and prior therapies are permitted. At enrollment pts have a baseline PSMA, which is repeated every 6 months (mos) if positive. If negative PSMA is done annually. CT and bone scan are also repeated annually. Pts are allowed to have radiation therapy or systemic therapies for ≤6 mos and remain on-study. Up to 350 pts will be enrolled and followed for up to 5 years. Results: Over 120 pts have enrolled since 3/2023 and 86 pts are evaluable after the 6-month PSMA scan/follow-up. The pts have a median age of 71 years, PSA=3.05, PSA doubling time=11.1 mos (29% less than 6 mos). In an overlapping descriptive analysis 10 pts were PSMA- and 17 pts had only local disease. For PSMA+ LNs, 17 pts had 1 LN, 9 pts had 2-3 LNs+, 5 pts had 4 LNs+, and 18 pts had 5+ LNs. 7 pts had bone findings, but negative bone scan. 4 pts had PSMA+ serosal nodules. 4 pts had radiation to solitary LNs. 1 pt elected androgen deprivation and 1 pt had salvage radiation. 4 pts enrolled on a clinical study at the NCI without androgen deprivation. At 6 mos PSMA scan only 1 pt had metastatic disease (bone scan findings). No pts had LNs beyond eligibility size criteria. No pts had new visceral findings. Conclusions: These preliminary data from an ongoing study suggest PSMA+ BCR is an indolent disease process and pts are at limited risk for clinically relevant progression within 6 mos. This study continues to accrue at the NCI and will seek to better define high risk PSMA+ BCR. These preliminary data may better inform the risk/benefits of aggressive treatment of PSMA+ BCR and clinical studies in PSMA+ BCR. Clinical trial information: NCT05588128 .