Risk of metachronous peritoneal metastases in patients with pT4a versus pT4b colon cancer: An international multicentre cohort study

Introduction: With evolving treatment strategies aiming at prevention or early detection of metachro-nous peritoneal metastases (PM), identification of high-risk colon cancer patients becomes increasingly important. This study aimed to evaluate differences between pT4a (peritoneal penetration) and pT4b (invasion of other organs/structures) subcategories regarding risk of PM and other oncological outcomes. Materials and methods: From eight databases deriving from four countries, patients who underwent curative intent treatment for pT4N0-2M0 primary colon cancer were included. Primary outcome was the 5-year metachronous PM rate assessed by Kaplan-Meier analysis. Independent predictors for meta-chronous PM were identified by Cox regression analysis. Secondary endpoints included 5-year local and distant recurrence rates, and 5-year disease free and overall survival (DFS, OS). Results: In total, 665 patients with pT4a and 187 patients with pT4b colon cancer were included. Median follow-up was 38 months (IQR 23-60). Five-year PM rate was 24.7% and 12.2% for pT4a and pT4b cat-egories, respectively (p = 0.005). Independent predictors for metachronous PM were female sex, right-sided colon cancer, peritumoral abscess, pT4a, pN2, R1 resection, signet ring cell histology and post -operative surgical site infections. Five-year local recurrence rate was 14% in both pT4a and pT4b cancer (p = 0.138). Corresponding five-year distant metastases rates were 35% and 28% (p = 0.138). Five-year DFS and OS were 54% vs. 62% (p = 0.095) and 63% vs. 68% (p = 0.148) for pT4a vs. pT4b categories, respectively. Conclusion: Patients with pT4a colon cancer have a higher risk of metachronous PM than pT4b patients. This observation has important implications for early detection and future adjuvant treatment strategies. (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).