Patients with ovarian cancer with defective DNA repair mechanisms derive substantial benefit from PARP inhibitor (PARPi) maintenance therapy. Both niraparib and olaparib are effective inhibitors of PARP, which exploit already defective DNA repair mechanisms (e.g., via BRCA mutations), particularly those with homologous recombination deficiency (HRD). These two PARPis have notably different toxicity profiles, with niraparib showing many more severe side effects. In this Ovarian Cancer Canada funded study, we will implement perform HRD testing for ovarian cancer patients in Saskatchewan with response to platinum-based chemotherapy. This information will provide personalized and precision estimates about the amount of benefit that can be expected from taking a PARPi. We will evaluate both treatment outcomes and quality of life in a real-world study setting, to inform future decision-making regarding efficacy, quality of life and cost-effectiveness of PARPi therapy, specifically for niraparib.

We hypothesize that for patients who are homologous recombinant proficient (HRP), the median 32.7-month incremental benefit (in delaying cancer progression) from taking a PARPi (niraparib is the only PARPi approved in this setting) will not be seen as being value-add when balanced by the decreased quality of life that accompanies the first 6-12 weeks of therapy. We also hypothesize that for women who are HRP, that PARPi therapy will not be cost-efficient.

Inclusion Criteria:

• Known or suspected stage 3/4 high grade serous or endometrioid ovarian cancer Able to provide oral consent and complete questionnaires in English as per study protocol

Exclusion Criteria:

• Ineligible for Maintenace PARPi therapy Refusal to undergo HRD testing