Objective  To assess the association between appendectomy and prognosis of secondary colorectal cancer.

  Methods  We retrospectively reviewed the data of 763 patients with colorectal cancer in The First Affiliated Hospital of Xi'an Jiaotong University from January 2013 to December 2016. Based on the inclusion and exclusion criteria, 89 patients who underwent appendectomy were included in the appendectomy group and 674 patients who did not undergo appendectomy were included in the non-appendectomy group. Overall survival rates were compared between the two groups, and the association between appendectomy and prognosis prediction was evaluated. Using the murine appendectomy model of chronic colitis-associated colorectal cancer, the relative abundance of Bacteroides, Prevotella, and Blautia in the feces of mice was compared using real-time fluorescent quantitative polymerase chain reaction (qPCR).

  Results   The 3- and 5-year overall survival rates were significantly lower in the appendectomy group than in the non-appendectomy group (61.8% vs. 75.1% and 46.4% vs. 69.3%, respectively), and the differences between the two groups were statistically significant (χ²=13.777, P<0.05). The analysis showed that appendectomy was an independent prognostic risk factor for colorectal cancer (HR=1.475, 95%CI: 1.030～2.114). The abundance of Prevotella and Bacteroides was higher and that of Blautia was lower in the feces of mice with colorectal cancer induced by azoxymethane (AOM)+ dextran sulfate sodium (DSS) after appendectomy.

  Conclusions   Appendectomy may be an independent risk factor for poor prognosis of colorectal cancer, and its potential mechanism is related to the enrichment of some inflammation-related bacteria in gut flora structure caused by appendectomy.