Biochemical failure after radical prostatectomy with PSA ≤ 1 ng/mL: prediction of PSMA-positive metastatic disease

OBJECTIVES: F-PSMA-1007 PET/CT (PSMA-PET), and (ii) to identify predictors of metastatic disease. METHODS: Fifty-five patients with biochemical recurrence (BCR, n = 47) or persistent disease (n = 8) following RP as their primary and only prior treatment were retrospectively included if presenting with PSA levels ≤ 1 ng/mL. Patients who received any other anticancer treatment were excluded. PSMA-PET findings were categorized as either local recurrence (i.e., prostatic fossa and seminal vesicles) or metastases. Predictors of PSMA-PET positivity were assessed with univariate and multivariate regression analyses both in the whole sample and in two subgroups defined according to PSA levels (Group A = PSA < 0.5 ng/mL; Group B = PSA between 0.5 and 1 ng/mL). RESULTS: Median PSA at the time of PET/CT was 0.37 ng/mL (range: 0.13-1.0). PSMA-PET was positive in 22/55 (40%) patients, 14/55 (25%) patients had metastatic disease. Overall, 31 PSMA-positive lesions were identified: 12/31 (39%) and 19/31 (61%) were local recurrences and metastases, respectively. In the whole cohort, ISUP grade > 3 (p = 0.003), pN1 status after surgery (p = 0.011), time to BCR ≤ 26 months (p = 0.03), and persistent disease (p = 0.003) were significantly associated with a higher rate of PSMA-positive metastases. At multivariate analysis, ISUP grade > 3 (p = 0.016) was the only independent predictor of metastases. Metastatic disease was detected in 8/38 (21%) patients in Group A and in 6/17 (35%) patients in Group B, respectively. In Group A, pN1 (p = 0.043) and persistent disease (p = 0.040) were significant predictors of metastases. In Group B, ISUP grade > 3 was the only predictor (p = 0.028). CONCLUSIONS: ISUP grade > 3, time to BCR ≤ 26 months, pN1 status, and persistent disease after surgery indicated a higher likelihood of PSMA-positive metastatic disease in a homogeneous cohort of patients with biochemical failure and low PSA values. pN1 status and persistent disease were significant predictors of metastatic disease also in patients with PSA levels < 0.5 ng/mL.