Background: Optimal sequencing of approved therapeutic agents in mCRPC is not known. The standard approach, is to treat until resistance then switch. The PRINT trial explores the efficacy of treating mCRPC with a rapidly-cycling, non-cross reactive regimen as a way to more effectively treat an intrinsically heterogeneous disease, to delay or prevent drug resistance, and minimize treatment toxicity. Methods: Patients were treated with 3 consecutive treatment modules, each of 12 weeks' duration: 1. abiraterone acetate 1000 mg PO daily and prednisone 5 mg PO BID; 2. cabazitaxel 20 mg/m2 IV and carboplatin AUC 4 IV q3 weeks; 3. enzalutamide 160 mg PO daily and radium-223 50 kBq/kg IV q4 weeks (in those with bone metastases). After completion of this 9 month regimen, patients are followed on ADT alone. Primary endpoint is PSA or radiographic time to disease progression. Results: From 3/2017 to 10/2018, 28 of 40 planned men with mCRPC were enrolled, 19 (67.9%) with bone metastases. PSA response rates ( > 90%/ > 50%), compared to baseline, following each treatment module: 1. 50%/78.6%; 2. 50%/92.7%; 3. 64.39%/92.7%. Currently, 14 patients have completed the study regimen with median follow up of 3.6 months, 8 of whom continue without any additional therapy. Of the patients evaluable for primary endpoint, median time to PSA progression is 96+ days (95% CI 82-110+ days). The regiment was well tolerated, grade 3/4 adverse effects include: hyperglycemia (17.9%), diarrhea (7.1%), anemia (3.6%), fatigue (3.6%), neutropenia (3.6%), thrombocytopenia (3.6%). Measurable response and molecular correlate data will be presented. Conclusions: Treatment of mCRPC with a rapidly-cycling non-cross reactive regimen is feasible, demonstrates significant antitumor benefits, and is well tolerated. Further follow up will determine if PRINT delays progression compared with standard approaches. Clinical trial information: NCT02903160