Tokai Pharmaceuticals (TKAI) shares have plunged in trading today after the company announced that it will stop its Phase 3 clinical trial, ARMOR3-SV, assessing lead product candidate galeterone compared to enzalutamide (XTANDI) in treatment-naive men with metastatic castration-resistant prostate cancer (mCRPC) whose tumors express the androgen receptor splice variant AR-V7. The company made its decision based on the recommendation from the independent Data Monitoring Committee that the trial was unlikely to meet its primary efficacy endpoint. Tokai intends to evaluate its ongoing ARMOR2 expansion in mCRPC patients with acquired resistance to enzalutamide and its planned study in patients who rapidly progress on either enzalutamide or abiraterone acetate (ZYTIGA).