Prediction of metachronous peritoneal metastases after radical surgery for colon cancer: a scoring system from an international multicenter cohort

Background: Since novel strategies for prevention and treatment of metachronous peritoneal metastases (mPM) are under study, it appears crucial to identify its risk factors. The aim of our study was to establish the incidence of mPM after surgery for colon cancer (CC) and to build a statistical model to predict the risk of recurrence. Materials and Methods: Retrospective analysis of consecutive pT3-4 CC operated at 5 referral centers (2014 – 2018). Patients who developed mPM were compared to patients who were PM-free at follow-up. A scoring system was built based on a logistic regression model. Results: Of the 1426 included patients, 74 (5.2%) developed mPM. Patients in the PM-group presented higher preoperative CEA (Median [IQR]: 4.5 [2.5 – 13.0] vs. 2.7 [1.5 – 5.9], P = 0.001) and Ca 19-9 (Median [IQR]: 17.7 [12.0 – 37.0] vs. 10.8 [5.0 – 21.0], P = 0.001), advanced disease (pT4a 42.6% vs 13.5%; pT4b 16.2% vs. 3.2%; P < 0.001), and negative pathological characteristics. Multivariate logistic regression identified Ca 19-9, pT stage, pN stage, extent of lymphadenectomy, and lympho-vascular invasion as significant predictors, and individual risk scores were calculated for each patient. The risk of recurrence increased remarkably with score values, and the model demonstrated a high negative predictive value (98.8%) for scores below 5. Conclusions: Besides confirming incidence and risk factors for mPM, our study developed a useful clinical tool for prediction of the risk of mPM. After external validation, this scoring system may guide personalized decision making for patients with locally advanced CC.