Prospective monitoring of biochemically recurrent prostate cancer (BCR) using prostate specific membrane antigen (PSMA) imaging: 21-month follow-up.

37 Background: The use of PSMA imaging is impacting the management of BCR, but it remains unclear if treatment escalation is required for PSMA+ BCR. While patients (pts) at the highest risk of death from prostate cancer (e.g. PSA Doubling Time (DT) less than 6 months) may benefit from therapy, the majority of BCR pts will not die of prostate cancer. Longitudinal data pf PSMA+ BCR is required to better understand risk stratification for PSMA+ BCR. Methods: NCT05588128 enrolls BCR pts after definitive therapy +/- salvage options. Pts are required to have a PSA>0.5 ng/ml, negative bone scan and computed tomography (CT; lymph nodes (LNs) up to 1.5 cm are permitted.) Prior therapies are permitted as long as testosterone>100 ng/dL. If initial PSMA scan is positive, PSMA scan is repeated every 6 months, but annually if negative. While on-study, patients may have systemic therapy for less than 6 month intervals and radiation (RT) is permitted. Results: 129 patients are evaluable with a median potential follow-up of 21.75 months (mos). Median baseline age=71 years, PSA=2.3 ng/ml and PSA DT=11.0 mos but 35% have PSA DT <6 mos. At baseline 23 pts (18%) had negative PSMA, 22 (17%) had prostate only findings, 24 (19%) had 1 LN, 9 (7%) had 2-3 LNs and 33 (26%) had 4+ LNs. Also, 19 pts (15%) had bone findings, 4 (3%) had PSMA+ serosal lesions and 1pt had PSMA+ pulmonary nodule. During the course of follow-up, 28 pts elected androgen deprivation therapy (ADT)-sparing NCI protocols, 1 pt had ADT, 1 pt had salvage RT, and 7 had RT to PSMA+ finding(s). Of 107 pts with PSMA+ findings, only 4 (3.7%) had developed metastasis on CT/bone scan with a median f/u of 21.75 mos. Conclusions: Most patients with BCR will not die of prostate cancer and it remains unclear how PSMA imaging will help risk stratify pts. This ongoing study demonstrates that with nearly 2 years of median follow-up, the risk of metastatic progression on CT or bone scan remains low even if patients have PSMA+ findings at baseline. These data do not support using PSMA imaging as the sole criteria to initiate therapy for BCR pts including those with numerous PSMA findings. This study continues to accrue patients at the National Cancer Institute, Bethesda, MD. Clinical trial information: NCT05588128 .