This is a Phase 2 open-label study of VT-464 in patients with progressive, metastatic castration-resistant prostate cancer (mCRPC) who have been previously treated with enzalutamide, female patients with triple negative, AR positive breast cancer and men with ER positive breast cancer. The study consists of five cohorts: patients in Cohort 1 must have never received prior chemotherapy. Patients in Cohort 2 must have received at least one (and not more) prior course of chemotherapy for CRPC. Women with TNBC will be stratified into two cohorts AR 1 to 9% (cohort 3) and AR > 10% (cohort 4). Cohort 5 will consist of men who have been diagnosed with ER+ breast cancer and have failed at least one prior endocrine therapy.