GSTM1 and metastatic neoplasm: Baseline characteristics associated with OS benefits in univariate Cox regression analysis were Hb levels at mCRPC diagnosis (HR: 0.78, 95% CI: 0.64–0.95, P = 0.012) and metastatic disease at initial diagnosis (HR: 2.10, 95% CI: 1.10–4.10, P = 0.031).