Multi-omics evaluation of peritoneal fluid in gastroesophageal cancer (OMEGCA): protocol for a prospective multicentre cohort study to detect occult peritoneal metastases in patients undergoing curative-intent treatment

Introduction 

Early detection of peritoneal disease, especially micro-metastases, in patients with gastroesophageal adenocarcinoma is critical as it alters therapeutic intent, providing a vital opportunity to personalise treatment. However, our ability to accurately stage the peritoneum is inadequate. Tumour-derived DNA in peritoneal lavage fluid (ptDNA) has been suggested to be more sensitive than current methods to stage the peritoneum. Accordingly, this study will determine whether ptDNA is a biomarker of peritoneal micro-metastasis and evaluate its prognostic value in patients with gastroesophageal adenocarcinoma undergoing curative-intent treatment. 

Methods and analysis 

This will be an Australian multi-centre prospective observational cohort study enrolling patients undergoing routine staging laparoscopy and subsequent curative-intent treatment (either upfront surgery or perioperative chemo-/radiotherapy and surgery) for gastric and gastroesophageal junction adenocarcinoma. Tumour biopsies, blood and peritoneal lavage fluid will be collected at the time of staging laparoscopy for all patients. A subset of patients will have blood and peritoneal fluid collected at the time of surgical resection, and blood collected at the first post-operative clinic. These biospecimens will undergo genomic and methylomic analysis to detect tumour DNA. ptDNA status will be correlated to disease free survival, peritoneal-specific event free survival, overall survival, sites of treatment failure, histopathological features, and peritoneal lavage cytology status.