Bastiaenen, Vivian PAalbers, Arend G JArjona-Sánchez, AlvaroBellato, Vittoriavan der Bilt, Jarmila D WD'Hoore, André DEspinosa-Redondo, EstherKlaver, Charlotte E LNagtegaal, Iris Dvan Ramshorst, Bertvan Santvoort, Hjalmar CSica, Giuseppe SSnaebjornsson, PeturWasmann, Karin A T G Mde Wilt, Johannes H WWolthuis, Albert MTanis, Pieter J2023-02-092023-02-092021-05-15http://hdl.handle.net/10668/17830With evolving treatment strategies aiming at prevention or early detection of metachronous 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. 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 metachronous 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). 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 categories, 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 postoperative 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. 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.enAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/Locally advanced colon cancerOncological outcomesPeritoneal metastasesSurvivalT4 colon cancerAbdominal AbscessAdenocarcinomaAgedCarcinoma, Signet Ring CellChemotherapy, AdjuvantCohort StudiesColon, AscendingColon, TransverseColonic NeoplasmsDisease-Free SurvivalFemaleHumansInternationalityMaleMiddle AgedNeoadjuvant TherapyNeoplasm InvasivenessNeoplasm Recurrence, LocalNeoplasm StagingPeritoneal NeoplasmsRisk FactorsSex FactorsSurgical Wound InfectionSurvival Rateresearch article34030920open access10.1016/j.ejso.2021.05.0091532-2157http://www.ejso.com/article/S0748798321004856/pdf