患上克罗恩病的患者经常患有会突破肛周的疾病。他们患肛门直肠癌的风险尚不确定。我们的目标是在拥有肛周瘘的CD患者的基于人口的队列中检测肛门直肠癌的长期风险。我们的研究对象为1978年至2018年在丹麦居住的所有15岁及以上的个体（n = 7,987,520）。我们通过丹麦全国患者登记簿（NPR）识别所有患有CD和肛周瘘的患者，以及从一般人群中选择50名非炎症性肠病（IBD）的个体。利用Cox回归分析，我们比较了CD瘘患者和非-IBD个体之间患肛门直肠癌的风险。所有CD患者均使用国际疾病分类代码进行识别，并从NPR中提取其数据。主要的结果指标为肛门直肠癌的病例。在随访期间，2786名患有CD和肛周瘘的患者和139,300名非-IBD个体被随访了1,553,917人年。在随访期间，肛门直肠癌在19名CD患者中（0.68％）和340名非-IBD个体中（0.24％）观察到，对应于CD瘘患者肛门直肠癌风险增加2.9倍的危险比（HR 95％CI1.80-4.53），尤其是肛门癌（HR 15.13，95％CI 6.88-33.31 ），CD瘘诊断至肛门直肠癌平均时间为6.7（SD 6.5）年。 女性的风险略高于男性，与肿瘤坏死因子-α抑制剂的治疗无明显关系。使用CD非-瘘患者进行比较的敏感性分析结果相似。无法获取有关吸烟和人乳头瘤病毒感染的个体数据。与一般人群相比，患有CD和肛周瘘的患者患肛门直肠癌的风险增加三倍。在具有长期瘘（> 6年）的患者中，需要对2160名患者进行监测才能检测到一例肛门直肠癌病例。©2023英国与爱尔兰大肠直肠病协会。

Patients with Crohn's disease (CD) often suffer from perianal fistulizing disease. Their risk of anorectal cancer remains uncertain. We aimed to examine the long-term risk of anorectal cancer in a population-based cohort of CD patients with anorectal fistula.Our study population covered all individuals (n = 7 987 520) aged 15+ years living in Denmark from 1978 to 2018. We identified all patients with CD and anorectal fistula in the Danish National Patient Register (NPR) and 50 matched noninflammatory bowel disease (IBD) individuals from the general population. Using Cox regression analyses, we examined the risk of anorectal cancer in CD fistula patients versus non-IBD individuals. All patients with CD were identified using codes from the International Classification of Diseases and their data extracted from the NPR. The main outcome measure was cases of anorectal cancer.A total of 2786 CD patients with anorectal fistula and 139 300 non-IBD individuals were followed for 1 553 917 person-years. During follow-up, anorectal cancer was observed in 19 CD patients (0.68%) and 340 non-IBD individuals (0.24%), corresponding to a 2.9-fold increased hazard ratio (HR) of anorectal cancer in CD fistula patients (95% CI 1.80-4.53), with a particularly high risk of anal cancer (HR 15.13, 95% CI 6.88-33.31) and a mean time from CD fistula diagnosis to anorectal cancer of 6.7 (SD 6.5) years. The risk was slightly higher in women than men and had no apparent relation to treatment with tumour necrosis factor-α inhibitors. Sensitivity analyses using CD nonfistula patients for comparison revealed similar results. Individual data on smoking and infection with human papilloma virus were not available.Patients with CD and anorectal fistula have a three-fold increased risk of anorectal cancer compared with the general population. The number needed to surveil to detect one case of anorectal cancer in this patient population was 2160 patients per year in patients with long-standing fistula (>6 years).© 2023 Association of Coloproctology of Great Britain and Ireland.