Appendectomy Mitigates Ulcerative Colitis Activity and Delays Colorectal Cancer Onset: A Retrospective Cohort Study.

Objective: Ulcerative colitis (UC) is an idiopathic inflammatory disease with rising global incidence, influenced by genetic, environmental, and immunological factors whose interactions remain unclear. Although the appendix appears to influence UC onset and disease activity, few studies have investigated how the timing of appendectomy affects disease activity and colorectal cancer risk. This study aimed to clarify the impact of appendectomy on disease activity and colorectal cancer risk in patients with UC.

Methods: We retrospectively analyzed 368 patients with UC treated at Osaka University Hospital and Kinshukai Infusion Clinic between April 2008 and December 2023. Participants were divided into two groups, namely the appendectomy (n=18) and non-appendectomy groups (n=350). We compared background characteristics, clinicopathological factors, and disease course, including Partial Mayo scores, relapse rates, proximal disease extension, medication use, and colorectal cancer development.

Results: The appendectomy group showed significantly lower Partial Mayo scores at the most severe flare (4.5 vs. 8; p<0.001), fewer relapses (p=0.016), lesser proximal disease extension (p=0.049), and lower use of steroids (p=0.032) and biologics or small molecules (p=0.006). Although colorectal cancer incidence was similar in the groups, the appendectomy group had a significantly longer duration from UC diagnosis to cancer diagnosis (29.3±16.0 vs. 16.0±9.9 years; p=0.033). Patients who underwent appendectomy after UC diagnosis exhibited milder disease activity, while those who underwent appendectomy before diagnosis were older at UC onset (p=0.004).

Conclusions: Appendectomy is associated with milder UC activity and may delay disease onset. These findings offer insights into UC pathogenesis and suggest potential preventive approaches.