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

45 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+ recurrent prostate cancer (PSMArpc) 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. PSMArpc 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 scans 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 100 pts have enrolled since 3/2023 and 73 pts were evaluable after the 6-month PSMA scan/follow-up. The pts had a median age of 71 years, PSA=2.8, PSA doubling time=11.1 mos (30% less than 6 mos). In an overlapping descriptive analysis 10 pts were PSMA- and 15 pts had only local disease. For PSMA+ LNs, 15 pts had 1 LN, 8 pts had 2-3 LNs+, 4 pts had 4 LNs+, and 16 pts had 5+ LNs. 6 pts had bone findings, but negative bone scan. 3 pts had PSMA+ serosal nodules. After baseline PSMA 3 pts had radiation to solitary LNs, only 1 resolved/PSA declined. 1 pt elected androgen deprivation and 1 pt had salvage radiation. 4 pts enrolled in a clinical study at the NCI without androgen deprivation. At 6 mos PSMA scan only 2 pts had metastatic disease, both with bone scan findings, no pts had LNs beyond eligibility size criteria, and no pts had new visceral findings. Conclusions: These preliminary data from an ongoing study suggest PSMArpc 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 PSMArpc. These preliminary data may better inform the risks/benefits of aggressive treatment of PSMArpc and clinical studies in PSMArpc. Clinical trial information: NCT05588128 .