Risk factors for appendiceal and colorectal peritoneal metastases.
Early diagnosis to target minimal volume disease has received increased attention in the management of appendiceal and colorectal peritoneal metastases (PM). This study aimed to identify risk factors for appendiceal, colon and rectal PM. Data were retrieved from the Swedish Colorectal Cancer Registry for all patients undergoing bowel resection of appendiceal and colorectal tumours, in Sweden, 2007-2015. Risk factors for synchronous and metachronous PM were analysed with multivariate logistic and Cox proportional hazard regression models. Synchronous PM was most common in appendiceal cancer (23.5%), followed by colon (3.1%) and rectal (0.6%) cancer. The 5-year cumulative incidence was 9.0% for appendiceal, 2.5% for right colon, 1.8% for left colon and 1.2% for rectal cancer. In appendiceal cancer (n = 327), T4, N2, mucinous tumour, and non-radical surgery were associated with PM. In colon cancer (n = 24,399), synchronous PM were primarily associated with T4 (OR 18.37, 95% CI 8.12-41.53), T3 and N2 but also with N1, right-sided tumour, mucinous tumour, vascular and perineural invasion, female gender, age <60 and emergency surgery. These factors were also associated with metachronous PM. In rectal cancer (n = 10,394), T4 (OR 19.12, 95% CI 5.52-66.24), proximal tumour and mucinous tumour were associated with synchronous PM and T4 and mucinous tumour with metachronous PM. This study shows that appendiceal cancer, right-sided colon cancer, advanced tumour and node stages and mucinous histopathology are the main high-risk features for PM and should increase the awareness of current or future PM.