The OC3 was started in 2012 with the objective to study the etiologic heterogeneity of ovarian cancer in multiple cohorts and to build the infrastructure of the Ovarian Cancer Cohort Consortium (OC3). The OC3 is an international consortium of cohort studies designed to address scientific aims important for understanding ovarian cancer risk, early detection, tumor heterogeneity, and prognosis that are only feasible in a consortium setting.