Sunitinib maintenance therapy after response to docetaxel in metastatic castration resistant prostate cancer (mCRPC)

Background Docetaxel is a standard first-line treatment option for men with metastatic castration resistant prostate cancer (mCRPC). Sunitinib is attractive as a maintenance therapy due to its mechanism of action, oral route of administration, and acceptable toxicity profile. We designed a phase II study of sunitinib in patients with mCRPC who responded to docetaxel. Methods Patients with responding or stable disease at the completion of docetaxel treatment received 50 mg of sunitinib on 4 week on 2 week off cycles. Treatment continued until disease progression (either by RECIST 1.1 criteria or by cancer related symptomatic progression), intolerable toxicity, start of new cancer therapy, withdrawal of consent, or death. The primary endpoint was progression free survival. Secondary endpoints included PSA response rate and safety. Results Twenty-three patients were enrolled and treated. The mean number of prior cycles of docetaxel given was 8.6 (range 4–12). The median number of cycles of sunitinib administered was 4 (range 1–11). Adverse events were generally grade 1–2 with 12 % grade ≥ 3 which were of a type and severity expected for sunitinib. Median PFS was 4.4 months (95 % CI: 1.6–5.1). Most patients had immediate PSA increases without other evidence of disease progression, with the mean increases in PSA over baseline being 197 %, 342 %, and 1437 % in Cycles 1, 2, and 3, respectively. Conclusion Sunitinib was tolerable as maintenance therapy but median PFS was significantly lower than the predefined threshold of 6 months.