This study (DARE part 1) is a single-center, retrospective, observational feasibility study promoted by the Fondazione Policlinico Universitario Agostino Gemelli IRCCS and co-funded by Fondazione AIRC, aimed at evaluating the clinical utility of circulating tumor DNA (ctDNA) for the assessment of minimal residual disease (MRD) in patients with epithelial ovarian cancer (EOC). In early-stage EOC, the current standard of care consists of complete surgical staging followed by platinum-based adjuvant chemotherapy in high-risk patients; however, the benefit of adjuvant treatment remains controversial in optimally staged cases, as no clear overall survival advantage has been demonstrated. Previous evidence has highlighted the limitations of conventional staging and the need for more accurate biomarkers to identify patients at higher risk of recurrence. ctDNA has emerged as a promising non-invasive biomarker for MRD detection and prognosis in several malignancies, including EOC, but its role in early-stage disease following curative surgery is still uncertain and has not yet been explored in registered studies guiding adjuvant treatment decisions.

The study will retrospectively analyze paired pre-operative (T0) and post-operative (T1, 4-7 weeks after surgery) plasma samples from 50 patients with epithelial ovarian cancer (excluding mucinous histology) who underwent surgery with curative intent and achieved no macroscopic residual disease. All samples were previously collected between January 2022 and June 2025 within other approved clinical studies and are stored in the institutional biobank. ctDNA analysis will be performed using an advanced next-generation sequencing (NGS) platform integrating genomic and epigenomic profiling, with laboratory analyses conducted by Guardant Health, while clinical and correlation analyses will be carried out by the promoting center. The primary endpoint is ctDNA clearance, defined as a binary change in ctDNA detectability between the pre- and post-surgical timepoints. Secondary endpoints include the correlation of ctDNA status with clinicopathological characteristics such as tumor grade, histological subtype, and FIGO stage, as well as the association between ctDNA detectability and progression-free survival. Statistical analyses will compare paired ctDNA measurements using McNemar's test, while associations with clinical variables and survival outcomes will be explored using logistic regression and Cox proportional hazards models supported by Kaplan-Meier estimates.

Inclusion Criteria:

• Epithelial ovarian cancer but mucinous histotype
• Available matched pre-operative and post-operative (4-7 weeks after surgery) plasma samples
• Minimum 4 ml of plasma each timepoint
• FIGO 2014 stage I-IV addressed to surgery with curative intent (no gross residual disease after surgery)

Exclusion Criteria:

• Absence of clinical data
• Less than 6 months of follow-up from surgery
• Diagnosis of other malignancies in the previous 5 years
• Absence of one or both of the prespecified timepoints

Patients with early-stage epithelial ovarian cancer (EOC) for whom blood samples collected between January 2022 and June 2025 are available.