Colorectal cancer is a leading cause of cancer-related mortality worldwide. Twenty percent of the patients with CRC develop distant metastases. Among them, 50% have liver metastases (LM) and 25% have peritoneal metastases (PM). Half of these metastatic patients will present with liver-only hepatic metastases (HM) and a quarter will have just peritoneal metastases (PM). The peritoneum representing the second metastatic site in frequency. Patients with colorectal PM have a dismal prognosis in comparison with other metastatic sites. For patients with limited resectable peritoneal disease, surgery remains the only potentially curative option. The two major prognostic factors in patients undergoing cytoreductive surgery (CRS) for PM are the extent of the disease, as evaluated by the peritoneal cancer index (PCI) and the completeness of the resection. In patients undergoing complete macroscopic CRS, the 5-years overall survival (OS) is up to 45% in patients with a PCI \<6, whereas OS falls to just 9% when PCI is \>19. At the present time, however, only a minority (16%) of the patients who undergo surgery with a curative-intent for PM are cured, as indicated by disease-free survival (DFS) \>10-years. Despite an aggressive combined approach (surgery and chemotherapy), most of these patients will die from loco-regional and/or systemic recurrence. This emphasizes the needs for a better characterization of the disease and for identification of more accurate selection criteria for surgery.

Very few studies have explored the pathophysiological mechanisms of PM development and progression. The main mechanism of reported peritoneal dissemination that has been reported is a stepwise dissemination including the exfoliation of tumoral cells from the primary tumour into the peritoneal cavity. The pathophysiological mechanisms underlying systemic dissemination in patients presenting with PM are also poorly understood. The most well-known lymphatic dissemination pathways from the peritoneum into supra-diaphragmatic lymph nodes (LNs) are the retroperitoneal lymphatic pathway and the cardio-phrenic LNs. The presence of involved cardio-phrenic LNs is predictive of PM involvement. However, detection of these LNs is based on imaging that has a limited sensitivity (65%) and surgical access requires the opening of the diaphragm.

Recently, the investigators reported, for the first time, a new lymphatic route of systemic dissemination of colorectal PM. The investigators reported LN metastases in the inferior epigastric LN basin (IELN). In this series, metabolic and morphologic imaging were not able to preoperatively predict the status of IELN. These LNs represent potential predictive factors of survival in patients treated for colorectal PM. The advantage of this LN basin is its easy surgical access that allows resection without increasing postoperative complications. The exact conditions for dissemination in IELN and their prognostic role remain undetermined.

The primary objective of this study is to evaluate the incidence of IELN basin involvement in patients with colorectal PM undergoing complete CRS. The secondary objectives are to evaluate the capacity of preoperative imaging to detect these lesions and to define conditions for IELN involvement.