In subgroup analysis, in patients with bone metastasis at diagnosis and RB1 expression lower than median, mean time to CRPC was significantly shorter (mean was 17.6 months; 95% CI: 6.0–29.1) compared to patients with high expression of RB1 (mean was 39.8, 95% CI: 29.5–50.1), as shown in the Kaplan-Meier survival curve analysis (p = 0.017, Fig. 3A). This evidence concerns the gene RB1 and bone metastasis.