Clinical and Pathological Risk Factors for Peritoneal Metastases in a Surgical Series of T4 Colorectal Cancers

<b>Background:</b> T4 colorectal cancer (CRC) is associated with an increased risk of peritoneal metastases (PM), but it is currently not possible to accurately predict which patients with T4 CRC develop PM. We investigated the occurrence and risk factors for PM in these patients. <b>Methods</b>: A mono-institutional prospective database of 352 patients undergoing T4 primary CRC resection from 2012 to 2021 was reviewed. Clinico-pathological variables potentially associated with synchronous or metachronous PM were tested by univariate and multivariate analyses. <b>Results</b>: The prevalence of synchronous PM was 73/352 (20.7%) and was significantly associated with age (<i>p</i> = 0.037), primary site (<i>p</i> = 0.002), positive nodes (<i>p</i> = 0.005), elevated CA19.9 (<i>p</i> = 0.001), and non-intestinal histology (<i>p</i> = 0.001). After a median follow-up of 35.9 months (95% confidence interval [CI] = 29.5-44.9), metachronous CRC-PM occurred in 36/164 patients (22.0%) with available data, accounting for a three-year cumulative incidence of 21.5% (95% CI = 14.3-28.1). Metachronous CRC-PM occurred in 3/48 patients (6.2%) with negative nodes and normal CEA, as compared with 33/116 patients (28.4%) with positive nodes and/or elevated CEA (<i>p</i> < 0.001). Combined nodal and CEA status (hazard ratio [HR] = 1.27; 95% CI = 1.02-1.59; <i>p</i> = 0.033), postoperative chemotherapy (HR= 0.51; 95% CI = 0.33-0.77; <i>p</i> = 0.001), and positive resection margins (HR = 2.01; 95% CI = 1.20-3.39; <i>p</i> = 0.008) were significantly associated with PM. <b>Conclusions</b>: The peritoneum is a major site for treatment failure in T4 CRC. Patients with normal CEA and negative lymph nodes are associated with a significantly lower risk for metachronous CRC-PM. These findings may help in refining patient selection for integrated approaches aiming at the prevention or early treatment of CRC-PM, which are pending validation in prospective studies.