The purpose of this study is to evaluate the prevalence of folate receptor alpha (FRα)-positive status (≥75% viable tumor cells with moderate (2+) and/or strong (3+) membrane staining) in participants with high-grade serous ovarian, fallopian tube, and primary peritoneal cancer, stratified by time of sampling (initial diagnosis versus relapse), adhering to Ventana folate receptor alpha (FOLR1) RxDx (prescription diagnosis) assay Interpretation Guidance.

Inclusion Criteria:

• Relapsed ovarian, fallopian tube and primary peritoneal cancer
• Histologically high-grade serous carcinoma
• Presence of archived surgical tissue samples from participants with epithelial ovarian cancer at diagnosis and at 1st recurrence in the same participants
• Available samples collected from January 1st, 2016 to study start date (defined as study site initiation visit date) that are considered adequate for the Ventana folate receptor alpha (FOLR1) RxDx assay by the site pathologist

Exclusion Criteria:

• Histological ambiguous diagnosis upon review
• Diagnosis based on cytology and without any biopsy or surgical specimen
• Other histotypes than high grade serous ovarian cancer, fallopian tube cancer and primary peritoneal cancer
• Archival or recurrent sample for the same participant not available

The study will be performed on archived tissue samples from approximately 200 eligible female adult participants with relapsed high grade serous epithelial ovarian cancer.