This phase II single-arm trial investigated the activity of 6MP 55–75 mg/m2 per day, and methotrexate 15–20 mg/m2 per week in advanced breast or platinum-resistant ovarian cancer patients with a BRCA1/2 germline mutation, who had progressed after ≥1 previous line of chemotherapy. Here, BRCA1 is linked to ovarian cancer.