Incidence of Appendix Cancer after Surgery for Colorectal Cancer: Should the Appendix be Prophylactically Removed During Surgery for Colorectal Cancer?

Abstract Introduction Retrospective cohort studies with limited sample sizes suggest that the incidence of appendix cancer may be increased in patients having surgery for colorectal cancer. Aims To determine whether patients who underwent surgery for colorectal cancer are at higher risk of appendix cancer. Methods Cases of colorectal and appendix cancer were identified from the NICER (National Institute for Cancer Epidemiology and Registration, Switzerland) database based on ICD-10 codes for the period 2009-2019. Incidental cases of appendix cancer (all histological types) were extracted from patients who underwent surgery for colorectal cancer and from the general population followed by cantonal cancer registries. Standardized incidence ratios were calculated. Results Twenty-eight thousand nine-hundred and thirty-four cases of colorectal cancer and 1,350 cases of appendix cancer were identified over the study period (10 years). After exclusion of cases of appendix cancer, 22,705 patients underwent surgery for colorectal cancer (at-risk population). In these patients, 43 cases of appendix cancer occurred over the follow-up period, including 35 NETs. In the reference population without any history of surgery for colorectal cancer, 1,305 incidental cases of appendix cancer occurred during the same period. This corresponds to an age-standardized incidence of 20.52 per 100,000 person-year in the at-risk population, and of 1.61 per 100,000 person-year in the reference population. The age-standardized incidence ratio for appendix cancer is 12.74 (95% CI: 12.02-13.45) in the at-risk population when compared to the reference population. However, most of these cases were synchronous cancers. To exclude potential information bias, a sensitivity analysis including only cases of left-sided colorectal cancer (colon and rectum) was performed. In this population, the age-standardized incidence ratio for metachronous appendix cancer is 8.67 (95% CI: 7.13-10.20). Conclusions The incidence of appendix cancer is increased in patients having surgery for colorectal cancer. The incidence may, however, be too low to consider routine prophylactic appendectomy during surgery for colorectal cancer.