Prognostic potential of PROSTest for predicting outcome in ADT-treated Black South African prostate cancer patients.

5104 Background: Prostate cancer (PCa) is the second most common cancer in men with disproportionately aggressive disease observed in black African and Caribbean men. Androgen deprivation therapy (ADT) is commonly used as treatment but there is no personalized strategy to guide patient selection. We investigated the prognostic value of PROSTest before ADT initiation and after the first ADT cycle. Methods: We performed a descriptive study of PROSTest with cross-sectional and longitudinal arms in black PCa patients receiving or intended to receive ADT. An ADT-naïve PCa cohort ( n =50) intended to start ADT was enrolled as well as an ADT-exposed cohort ( n =80) 6-12, 12-24 or >24 months after starting ADT. Goserelin acetate alone or in combination with cyproterone acetate was administered. The cohorts were followed up 4-monthly for 36 months with evaluation of survival and treatment response (responding, in remission, recurrence, progression, castration resistance). PSA levels were measured using the Architect Total PSA chemiluminescent immunoassay. Whole blood samples were collected into deproteinizing RNA-buffered tubes for determination of the PROSTest activity score using a multiplexed PCR assay. Statistical analysis used non-parametric statistics and Fisher’s exact test in GraphPad Prism v8. Results: Untreated metastatic PCa patients had the highest baseline PROSTest scores (71.8-85.3). Untreated patients with organ-confined disease were subdivided into group A (PROSTest scores ≤32) and group B (PROSTest scores ≥70). ADT-treated patients enrolled after starting ADT were subdivided into group C (PROSTest scores 9.8-58.3) and group D (PROSTest scores 70.0 – 90.2). Groups A and C showed improved survival and lower rates of recurrence, progression and castration resistance at 36 months compared to groups B and D (p<0.05). Patients that required treatment re-initiation or escalation due to rising PSA all had high enrolment PROSTest scores ≥70. The groups did not differ significantly in terms of age, CAPRA score, Gleason grade, PSA levels, nadir PSA, time to nadir or SUVMAX ( p >0.05). Conclusions: The PROSTest activity score determined pre- or post-ADT (first cycle) identifies PCa patients at risk for poor treatment outcomes.