Response rates to second-line platinum-based therapy in ovarian cancer patients challenge the clinical definition of platinum resistance

The aim of this study was to compare response rates and survival in women with "platinum resistant" epithelial ovarian cancer (EOC) who received further platinum-based or non‑platinum chemotherapy for treatment at first relapse.Patients with high-grade EOC (including fallopian tube and peritoneal cancer) of all histologies recruited to the Australian Ovarian Cancer Study (AOCS) and treated with platinum-based primary chemotherapy were included. Response to second-line chemotherapy, overall survival (OS) and survival after treatment for first progression (OS2) were determined in all histologies and separately in women with high-grade serous tumors.Of the 341 patients classified as platinum-resistant by the 6-month threshold, 243 (71%) were treated with chemotherapy at relapse. CA-125 response rates to platinum-based chemotherapy were significantly higher compared to non‑platinum chemotherapy (51% vs 21%, P 0.001). Among patients with a platinum-free interval (PFI) of 3-6 months, OS2 in patients treated with platinum was significantly longer compared to individuals receiving non‑platinum-based treatment (median 17.67 months, 95% CI: 14.79-20.75 vs. 10.62 months, 95% CI: 8.02-12.72, P = 0.022). The patterns were similar when restricted to patients with high-grade serous histology. In patients with PFI3 months, there was no significant difference in response or survival according to type of second-line treatment.Our findings further question the use of a 6-month PFI as an arbitrary threshold for subsequent treatment decision-making. Some patients considered "platinum resistant" still derive clinical benefit from platinum-based chemotherapy. Biomarkers of platinum sensitivity are needed in clinical practice to identify potential responders who should be offered re-treatment with platinum.