The starting dose cohort in the dose escalation stage will be 50 mg GT0918 (proxalutamide) PO once daily administered to 3 subjects in a fasted state. The next dose cohort in the dose escalation stage will be 100 mg PO once daily administered to 6 subjects in a fasted state with escalation to the following dose levels, each having a total of at least 6 subjects per cohort: 200 mg, 300 mg, 400 mg, and 500 mg. Dose escalation can occur after a minimum of 3 subjects in the 50 mg dose level have completed 28 days of treatment, no DLTs have occurred and the safety review of the cohort has been performed. Dose escalation in the remaining cohorts can occur after a minimum of 6 subjects have completed 28 days of treatment, either no DLTs or ≤1 subject has a DLT, and the safety review of the cohort has been performed.