Peritoneal Metastases in Stage II-III Colon Cancer Represent a Blind Spot for Circulating Tumor DNA Surveillance.

While circulating tumor DNA (ctDNA) may guide adjuvant therapy in stage II-III colon cancer, detection largely hinges on systemic tumor shedding. In a secondary analysis of three prospective ctDNA studies, peritoneal metastases occurred in up to 9.4% of patients, were predominantly isolated, and were enriched among ctDNA-negative recurrences. Molecular and clinical data demonstrate reduced ctDNA levels in peritoneum-only disease, identifying a surveillance blind spot with direct implications for high-risk patients.