Association of prostate specific antigen (PSA) doubling time (DT) and prostate specific membrane antigen (PSMA) findings in biochemically recurrent prostate cancer (BCR).

33 Background: Historically, PSA DT can be prognostic for metastasis free survival in BCR (as defined on computed tomography (CT) and bone scan). PSA DT is also an important tool in risk stratification in BCR to identify which patients (pts) require therapy (e.g. pts with a PSA DT>6 months). The emerging use of PSMA imaging creates another tool to assess BCR pts, but there is no data on the association of PSA DT and PSMA findings. Methods: NCT05588128 enrolls BCR pts after definitive +/- salvage therapies. Pts must have 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. All patients undergo a baseline PSMA PET scan, along with measurement of PSA and PSA DT. Here we describe the relationship between baseline PSA metrics and baseline PSMA imaging findings in patients with BCR. Results: 130 patients are currently evaluable with a median age= 71 years, baseline PSA of 1.95 ng/dL (range: 0.5 to 71) and PSA DT of 10.6 months (range 1.2 to 132) off therapy. Of all participants, 16.9% (n=22) had findings limited to the prostate bed and 34.6% (n=45) had PSMA+ avidity in the prostate bed with other findings. 42.3% (n=55) had PSMA + LNs, and 13.8% (n=18) had PSMA+ bone lesions. Four patients had serosal deposits with PSMA avidity, and one patient had a PSMA+ lung nodule. Conclusions: These data are the first to compare PSMA imaging results with corresponding PSA levels and PSA DT in a large cohort of patients with BCR. Results show that pts with historically favorable/long PSA DT may have high volume/bone+ findings on PSMA. There is no data to suggest treatment escalation is required in BCR pts with high volume PSMA findings, but long/favorable PSA DT. These results highlight the caveats of using PSMA imaging alone to drive treatment decisions in BCR without further data for how baseline PSMA imaging corresponds with long-term outcomes. Clinical trial information: NCT05588128 . PSMA PET+ lesion locations by PSA doubling time in patients with BCR prostate cancer (total n=130). PSA DT # Pts Median PSA PSMA Neg Prostate+ only Lymph Nodes+ ≥ 4 Lymph Nodes+ Bone+ ≥12 mo 52 3.55 9 (17.3%) 16 (30.8%) 24 (46.2%) 12 (23%) 6 (11.5%) 9 to <12 mo 20 1.56 2 (10%) 4 (20%) 11 (55%) 3 (15%) 3 (15%) 6 to <9 mo 17 0.9 5 (29.4%) 0 (0%) 12 (70%) 8 (47.1%) 2 (11.8*) <6 mo 41 2.1 5 (12.2%) 2 (4.9%) 28 (68.3) 15 (36.6) 7 (17.1)