Prediction of Peritoneal Dissemination of Digestive Tumors Through the Study of Circulating Tumor DNA

The peritoneum is a relatively frequent metastatic site in digestive tumors (colon, stomach, pancreas) and is characterized by a poorer prognosis compared with other metastatic sites such as the lung or liver. Its dissemination pathway is complex and most often involves crossing the hemato-peritoneal barrier. This type of metastasis is difficult to visualize on imaging at an early stage, and surgical exploration may be required. In gastric cancer in particular, exploratory laparoscopy is part of the initial staging work-up for locally advanced tumors to assess the presence or absence of peritoneal metastases. It is therefore important to develop new, less invasive detection or prediction methods.

Circulating tumor DNA (ctDNA) is a promising non-invasive blood biomarker that can assist clinicians as a prognostic/predictive biomarker and/or a tool for monitoring response to anti-tumor therapies. This marker is most often assessed in plasma, but recent data suggest that tumor DNA may also be detected in other biological fluids such as peritoneal fluid. A preliminary study conducted by our team showed the ability to detect tumor DNA in peritoneal fluid from patients with peritoneal carcinomatosis of various origins, with a sensitivity of 75%. In gastric cancer, a recent meta-analysis demonstrated an increased risk of peritoneal metastases when peritoneal tumor DNA was positive (RR 13.81 \[95% CI, 8.11-23.53\]), as well as a reduction in 3-year recurrence-free survival (RR 5.37 \[95% CI, 1.39-20.74\]) and overall survival (HR 4.13 \[95% CI, 1.51-11.32\]).

The objective of this cohort is to evaluate the prognostic impact of circulating tumor DNA (ctDNA) in plasma and/or peritoneal fluid on the risk of developing peritoneal metastases. The primary endpoint is: Peritoneal recurrence rate according to tumor DNA positivity status (positive vs negative).