The PROOV study is an open-label, monocenter, single-arm, prospective phase I/II trial with a safety lead-in, evaluating the feasibility of combining PARPi with HIPEC in stage III EOC patients. Phase I is a dose-finding phase with a time-to-event Bayesian Optimal Interval (TITE-BOIN) design, in which three doses of olaparib are evaluated to identify the optimal dose for the phase II part and future trials. The recommended phase II dose (RP2D) will be determined based on the experienced DLTs per dose level and the level of intra-tumor and systemic enzymatic PARP inhibition. During Phase II, the safety profile of the RP2D will be assessed in a total cohort of 40 patients. To provide a proof-of-concept, efficacy will be explored in both translational analyses and survival data.