Loss of 5-hmC is correlated with a shorter time to relapse following platinum-based chemotherapy and poor prognosis in patients newly diagnosed with HGSOC. A, Progression-free survival of patients with platinum response data (n = 59) shows a significant decrease in average time to disease relapse for patients with low 5-hmC (<2, n = 30) when compared to patients with high 5-hmC (≥2, n = 29). Patients with high 5-hmC levels experience a significantly longer time to initial disease relapse following platinum-based chemotherapy relative to low 5-hmC patients (**, P < 0.01). B, Kaplan–Meier survival curve of all patients with HGSOC included in the BWH TMA (n = 107). Patients with higher 5-hmC levels (primary tumor score ≥2, n = 54) have a significantly increased overall survival when compared with patients with low 5-hmC levels (primary tumor score <2, n = 53; ***, P < 0.0001).