LAUSR

5004 Background: Docetaxel (DOCE) is a standard of care in metastatic castration-resistant prostate cancer (mCRPC). Several retrospective cohort studies suggest a decrease in PC incidence and mortality with metformin (MET). MET has also demonstrated anti-tumor activity in PC preclinical models, with increase apoptosis when added to DOCE. The addition of MET could enhance DOCE efficacy in mCRPC patients (pts). Methods: TAXOMET is a phase II prospective multicentric randomized controlled trial. Non-diabetic mCRPC pts were assigned 1:1 to receive DOCE 75mg/m2 every 21 days + prednisone (P) 5 mg twice a day and either MET 850mg twice a day (arm A) or placebo (arm B), up to 10 cycles. The primary end point was PSA response rate (≥50% decrease). Main secondary endpoints included objective response rate (ORR, according to RECIST v1.1), clinical and biological progression-free survival (PFS), overall survival (OS), toxicity and quality of life (QoL). Comparisons between arm A and B were performed using Chi² test for qualitative data and Log-rank test for survival data. Results: From January 2013 to December 2015, 99 pts were randomized (50 pts in arm A and 49 pts in arm B) in 10 french centers, and 95 pts were evaluable. No difference was observed between arm A and arm B in PSA-response rate (72% in both arms), ORR (28% in both arms), clinical or biological mPFS (7.3 months vs 5.8 months p = 0.848) and mOS (24.2 months (95CI: 17.2 – 33.7) vs 19.7 months (95CI: 14.8 – 36.8), p = 0.53), respectively. There was no difference between arms in adverse events, except a trend for diarrhea to be more common with MET (70% in arm A vs 50% in arm B, p = 0.072), but few grade 3-4 events. There was no difference in QoL according to QLQ-C30 score between the two arms during the treatment period. Conclusions: This is the first prospective randomized controlled trial to evaluate the combination of MET with DOCE+P in mCRPC. The addition of MET has no meaningful clinical benefit in this setting. Clinical trial information: NCT01796028.