Outcomes of ovarian cancer patients treated with platinum or non-platinum based chemotherapy after PARP inhibitor maintenance.

5563 Background: PARP inhibitors (PARPi) are approved for maintenance treatment of platinum sensitive ovarian cancers either after front-line therapy or after treatment for recurrence. Current recommendations include retreatment with platinum-based chemotherapy (PC) after progression on maintenance PARPi. There exists a theoretical concern that progression of disease (POD) on PARPi is indicative of the development of platinum resistance due to similar DNA targets of platinum chemotherapy and PARPi. Our objective was to evaluate the response to subsequent chemotherapy in patients who progressed on PARPi maintenance. Methods: All patients with ovarian, fallopian tube, or primary peritoneal cancer treated with PARPi treatment from 2017 to 2021 at two academic tertiary care centers were retrospectively identified. Patients were assessed for treatment time on PARPi, time to POD on PARPi (PFS), type of chemotherapy regimen following PARPi maintenance, and time to disease progression on subsequent therapy following PARPi (PFS2). Comparative statistical analyses were performed with appropriate two-sided statistical tests. Time to progression on chemotherapy after PARPi was calculated using the Kaplan-Meier method. Results: A total of 83 ovarian cancer patients treated with PARPi were identified, and of these, 61 (73.5%) were treated with PARPi in the maintenance setting. Among the patients treated with PARPi maintenance, 22 (36.1%) remain on treatment. 19 (31.1%) patients were started on PARPi maintenance after front-line chemotherapy. While on PARPi maintenance, 63.9% discontinued PARPi, the majority due to POD, and 26.2% due to patient intolerance of side effects. Following POD, 21/29 (72.4%) received subsequent PC and 8/29 (27.6%) received non-platinum based chemotherapy (NPC). Treatment time, PFS, and PFS2 are listed in Table. Of the patients who received PC, 14/21 (66.7%) had a PFS2 of over six months and 5/21 (23.8%) had a PFS2 of over 12 months. Of the patients who received NPC, 7/8 (87.5%) had a PFS2 of over six months and 2/8 (25.0%) had a PFS2 of over 12 months. Conclusions: Following POD on PARPi, patients responded to both PC and NPC. Time to progression on subsequent chemotherapy after treatment with PARPi does not differ significantly between PC and NPC regimens. Many patients continue to see benefit from PC after PARPi maintenance. Retreatment with PC following POD on PARPi maintenance should still be considered.[Table: see text]