Malignancy rates in Crohn's disease patients with perianal fistula: A German retrospective cohort study

BACKGROUND: Patients with inflammatory bowel disease are at increased risk of colorectal and extra‐intestinal cancer. However, the overall cancer risk in patients with Crohn's disease (CD) with perianal fistulas (PF) (CPF) and those with CD without PF (non‐PF CD) is unclear. OBJECTIVE: To describe the prevalence and incidence of cancer in patients with CPF and non‐PF CD, and to estimate incidence rate ratio (IRR) of cancer between CPF and non‐PF CD groups. METHODS: A retrospective cohort study was conducted using the German InGef (Institute for Applied Health Research Berlin) research database. Patients with a CD record and PF from 1 January 2013 to 31 December 2014 were identified and followed up from 1 January 2015 until the first occurrence of cancer, end of health insurance contributing data, death, or end of study period (31 December 2020). Prevalence of any type of cancer including patients with CD diagnosed with cancer in the selection period and incidence of cancer excluding patients with CD diagnosed with cancer in the selection period were calculated. RESULTS: In total, 10,208 patients with CD were identified. Of 824 patients with CPF (8.1%), 67 had had a malignancy (6‐year period crude malignancy prevalence 8.13% [95% confidence interval (CI) 6.36%–10.21%]), which was lower than patients with non‐PF CD (19.8% [95% CI 19%–20.6%]). Incidence (per 100,000 person‐years) in patients with CPF was 1184 (95% CI 879–1561) and in non‐PF CD was 2365 (95% CI 2219–2519). There was no significant difference in the adjusted IRR of cancer for the CPF group compared with the non‐PF CD group (0.83 [95% CI 0.62–1.10]; p = 0.219). CONCLUSION: There was no significant difference in the incidence of any cancer in patients with CPF compared with non‐PF CD. However, patients with CPF had a higher numerical risk of cancer than the general German population.