Liquid biopsy in peritoneal fluid and plasma as a prognostic factor in advanced colorectal and appendiceal tumors after complete cytoreduction and hyperthermic intraperitoneal chemotherapy.

BACKGROUND: Positive cytology has been identified as an independent negative prognostic factor in patients with peritoneal metastases (PM) of colorectal origin. Liquid biopsy in plasma may detect increasing levels of circulating tumor DNA (ctDNA) and could help predict systemic relapse in patients with colorectal cancer, but little is known about the role of liquid biopsy in peritoneal fluid. The aim of this study was to evaluate the prognostic value of peritoneal fluid and plasma liquid biopsy in patients undergoing complete cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CC-HIPEC). METHODS: A longitudinal prospective study was designed in patients with KRAS-mutated colorectal or appendiceal primary tumor, including PM of colorectal origin, pseudomyxoma peritonei and patients at high risk of developing PM (selected for second-look surgery). Eleven patients were recruited according to inclusion and exclusion criteria. ctDNA from plasma and peritoneal fluid before and after HIPEC was studied by droplet digital PCR looking for KRAS mutation. A close follow-up was scheduled (mean of 28.5 months) to monitor for systemic and peritoneal recurrences. RESULTS: All patients with positive plasma postHIPEC had systemic relapse and four patients died as a result, while those with negative plasma postHIPEC did not relapse. Patients with negative peritoneal ctDNA after CC-HIPEC did not present peritoneal relapse. Of six patients with positive peritoneal ctDNA postHIPEC, two presented peritoneal recurrence and four systemic relapses. CONCLUSIONS: Treatment with CC-HIPEC does not always neutralize ctDNA in peritoneal fluid, and its persistence after treatment may predict adverse outcome. Despite being a proof of concept, an adequate correlation between liquid biopsy in plasma and peritoneal fluid with both systemic and peritoneal relapse has been observed.