The goal of this retrospective observational study is to evaluate the relationship between different dietary patterns (specifically low-carbohydrate diets) and the prognosis of patients with high-grade serous ovarian cancer (HGSOC) receiving first-line PARP inhibitor (PARPi) maintenance therapy. The main questions it aims to answer are:

• Is there an association between dietary patterns and patients' Progression-Free Survival (PFS)?
• Is there an association between dietary patterns and Overall Survival (OS)? This is a multicenter, retrospective cohort study. Researchers will review electronic medical records from 14 tertiary hospitals in China to identify women who received first-line PARP inhibitor maintenance for advanced high-grade serous ovarian cancer between 2020 and 2025, and collect information on baseline characteristics, treatments and follow-up outcomes.

Researchers will compare patients with a "low-carbohydrate diet pattern" to those with a "regular/high-carbohydrate diet pattern" to see if there are differences in treatment outcomes and survival.

Participants will:

• Have their clinical, pathological, and treatment data collected from electronic medical records.
• Complete a retrospective Food Frequency Questionnaire (FFQ) via phone or clinic visit to recall their dietary habits during the maintenance treatment period.
• Optionally provide a blood sample for nutrition and metabolic analysis. (For participants at the main study center only) No experimental drugs or specific diets will be given in this study. All anti-cancer treatments are decided by the treating physicians as part of routine clinical care.

Inclusion Criteria:

• Female patients aged 18 to <75 years.
• Histologically or cytologically diagnosed with primary high-grade serous ovarian cancer (HGSOC), fallopian tube cancer, or primary peritoneal cancer.
• Received initial tumor cytoreductive surgery (Primary Debulking Surgery or Interval Debulking Surgery) and first-line platinum-based chemotherapy, achieving Complete Response (CR) or Partial Response (PR).
• Received PARP inhibitors as maintenance therapy for the first time following the completion of first-line treatment.
• Complete clinical data available in the electronic medical records, including baseline characteristics, first-line treatment details, PARPi maintenance therapy information, and prognostic follow-up data.
• The patient (or primary caregiver) has normal communication abilities, voluntarily agrees to participate, and is able to cooperate in completing the retrospective Food Frequency Questionnaire (FFQ).

Exclusion Criteria:

• Clinical diagnosis only, without pathological or cytological confirmation.
• Non-high-grade serous histological subtypes (e.g., ovarian clear cell carcinoma, endometrioid carcinoma, mucinous carcinoma, low-grade serous carcinoma).
• Secondary or metastatic ovarian cancer (malignancy originating from other organs).
• Severe deficiency of key clinical or prognostic information that prevents assessment of the primary endpoint.
• Inability to accurately recall dietary information due to cognitive impairment, mental illness, or other reasons.
• Presence of severe metabolic or digestive system diseases during PARPi maintenance therapy that required specific restricted diets (e.g., insulin-dependent diabetes, dialysis-dependent renal insufficiency, short bowel syndrome, active Crohn's disease).
• Occurrence of significant physiological events during the study period that significantly altered dietary structure (e.g., major gastrointestinal surgery).

This study includes only women with ovarian, fallopian tube, or primary peritoneal cancer. These cancers arise in female reproductive organs, so only female patients who have been diagnosed with these conditions and received PARP inhibitor maintenance therapy are eligible for this study.

The study population consists of women with primary high-grade serous ovarian cancer, fallopian tube cancer, or primary peritoneal cancer who were treated at 14 tertiary hospitals in China. Eligible patients underwent primary or interval debulking surgery followed by first-line platinum-based chemotherapy, achieved complete or partial response, and then received a PARP inhibitor as first-line maintenance therapy between 2020 and 2025. Participants are identified from hospital electronic medical records, and those who can be contacted and are willing to participate will complete a retrospective food frequency questionnaire about their usual diet during PARP inhibitor maintenance.

It is currently undecided whether individual participant data (IPD) will be shared. The decision will be subject to compliance with the Data Security Law of the People's Republic of China and regulations on human genetic resources management. At this stage, the study protocol specifies that research results will be reported in aggregated summary forms to protect patient privacy. A final data sharing plan will be determined upon study completion in accordance with applicable laws and institutional policies.