Intraepithelial serous carcinoma of the endometrium: protocol for a prospective multicentre registry in the Netherlands.

introductionSerous endometrial intraepithelial carcinoma (SEIC) is a rare, non-invasive lesion of the endometrial epithelium, typically characterised by p53 abnormalities. Although regarded as a precursor lesion, recent classification systems increasingly position SEIC within the broader spectrum of serous carcinomas and current guidelines place non-invasive p53-abnormal serous lesions in an uncertain risk category due to limited outcome data. As a result, SEIC is not consistently addressed as a distinct diagnosis, contributing to variation in clinical management. Complete surgical staging, including pelvic and para-aortic lymph node assessment, is frequently performed, yet supporting evidence remains scarce. This study aims to collect longitudinal data to evaluate surgical management strategies in relation to clinical outcomes, survival and quality of life. METHODS AND ANALYSIS: This multicentre prospective observational cohort will enrol patients diagnosed with SEIC or equivalent non-invasive serous lesions who provide informed consent. Data will be collected using electronic case report forms (Castor Electronic Data Capture). Baseline clinical, pathological, molecular and treatment data will be collected, including imaging, histopathology, immunohistochemistry and molecular classification when available. Patient-reported outcomes will be assessed using the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire Core 30 (EORTC QLQ-C30), European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire Endometrial Cancer Module (EORTC QLQ-EN24) and EuroQol 5-Dimension 5-Level questionnaire (EQ-5D-5L) questionnaires at baseline, 6 months, 2 years and 5 years after diagnosis. The primary outcome is progression-free survival, secondary outcomes include overall survival, health-related quality of life and adverse events. Analyses will be primarily descriptive. Survival outcomes will be estimated using Kaplan-Meier methods, with Cox proportional hazards modelling used to explore predictors of outcome where feasible. ETHICS AND DISSEMINATION: The study will be conducted in accordance with the Declaration of Helsinki and applicable regulations. Ethical approval was obtained at the Erasmus MC (MEC-2025-0368). Results will be disseminated through peer-reviewed publications and scientific meetings. TRIAL REGISTRATION NUMBER: NCT06677242.