PRINT: Prostate cancer intensive, non-cross reactive therapy for CRP—Early observations of efficacy.

Abstract

89 Background: Optimal sequencing of therapeutic agents in mCRPC remains debated, but the standard approach is to treat with one agent until resistance is met before switching. PRINT explores the efficacy of treating mCRPC with a rapidly-cycling, non-cross reactive regimen as a way to more effectively treat intrinsic heterogeneity, delay/prevent drug resistance, and minimize toxicity. Methods: Enrolled patients all received 3 consecutive treatment modules, each 12 weeks: 1. abiraterone acetate 1000 mg PO daily + prednisone 5 mg PO BID; 2. cabazitaxel 20 mg/m2 IV + carboplatin AUC 4 IV q3 weeks; 3. enzalutamide 160 mg PO daily + radium-223 55 kBq/kg IV q4 weeks (in those with bone metastases). Upon completion of the 9-month regimen, patients are followed on ADT alone. Primary endpoint for the study is PSA or radiographic time to progression (TTP). Results: From 3/2017 to 10/2019, 35 of 40 planned men with mCRPC were enrolled, 25 patients have completed the 9-month study regimen and evaluable for TTP analysis. With median follow up of 52 weeks, median time to PSA progression after therapy completion is 15.5 weeks (95%CI; 5-26.1+ weeks). PSA response rates show successive improvements with each sequential treatment module (Table). Six (24%) patients continue on post-study surveillance with ADT alone, two of which have remained off any mCRPC agents for over a year (64+ weeks, 54+ weeks). In patients needing to restart therapy, experience with efficacy and tolerability of each agent while on the study, has helped inform subsequent mCRPC drug selection. The study regimen is well-tolerated, with few grade 3/4 AE’s: hyperglycemia (14.3%), diarrhea (5.7%), anemia (2.9%), fatigue (2.9%), neutropenia (2.9%), and thrombocytopenia (2.9%). Conclusions: Treatment of mCRPC with a rapidly-cycling non-cross reactive regimen demonstrates significant antitumor benefits, with potential for long-term suppression of disease. Further longitudinal follow up will determine if PRINT delays progression compared with standard approaches. Clinical trial information: NCT02903160. [Table: see text]