Adverse events in the placebo arm of SOLO2/ENGOT-Ov21 maintenance trial of olaparib in recurrent ovarian cancer

Background: In women with platinum sensitive recurrent ovarian cancer (PSROC) undergoing maintenance treatment, adverse events (AEs) not attributable to the current treatment are not well understood. We used data from SOLO2/ENGOT-Ov21 to evaluate AEs reported in the placebo arm and to explore their longitudinal trajectories. Methods: SOLO2/ENGOT-Ov21 (NCT01874353) randomly assigned 295 PSROC participants with a BRCA1/2 mutation to maintenance olaparib tablets (N = 196) or matching placebo (N = 99). For those assigned to placebo, we analyzed the AE (CTCAE v4.0) data including type, grade, time of onset and resolution, and attribution by investigator. Results: Amongst 99 participants who received placebo 788 AEs were reported (95 % reporting ≥1 AE). Twenty-two percent of participants reported at least one grade ≥ 3 AE. Grade ≥ 2 AEs that persisted for over 100 days affected 21 % of participants. Recurring grade ≥ 1 AEs were experienced by 44 % of participants. Study investigators attributed 25 % of all AEs to the placebo treatment, with neutropenia (88 %), nausea (52 %) and thrombocytopenia (50 %) most attributed. Three percent of participants had a dose reduction, 19 % had treatment delays, and 2 % had permanent treatment discontinuation, due to AEs attributed to placebo. Conclusion: Virtually all PSROC participants in the SOLO2/ENGOT-Ov21 experienced one or more AE whilst on placebo. Furthermore, study investigators attributed one quarter of AEs to be related to placebo therapy and dose alterations and treatment changes were made based on these AE. Further work is needed to improve measurement and categorization of AEs in trials of maintenance therapy in PSROC.