Perianal fistulising Crohn disease-associated malignancy: a multi-institutional study of histology, clinical features, and outcomes.

Perianal fistulising Crohn's disease (CD) is a debilitating complication of CD. Malignancies arising in this setting are rare and challenging to diagnose. In this study, we aimed to characterise the clinical, pathologic, and outcome features of perianal CD fistula-related malignancies (PCDFMs). We conducted a multi-institutional retrospective study (between 2005 and 2023) querying pathology databases of six academic centres for PCDFM. Only cancers arising in perianal fistulising CD were included. Clinical, imaging, pathologic, and follow-up data were collected and analysed. A total of 32 patients (19 males and 13 females) were identified. The median age at diagnosis was 53.6 years (range 30-74). Median duration of CD and fistula was 300 months (range 96-684) and 53 months (range 3-564), respectively. Thirty-one of 32 (96.9%) were symptomatic. Imaging was available in 27 patients (84.4%) and was abnormal in all cases. Serum carcinoembryonic antigen levels were available in 17 patients, of which 8 (47.1%) were elevated. Histologically, 26 cases (81.3%) were adenocarcinomas and 6 (18.8%) were squamous cell carcinomas. Twenty-three patients underwent resections, and 27 received chemotherapy with or without radiation. Pathologic staging was available in 19 patients: three had T4 disease, four had nodal disease, and one had distant metastasis. Median follow-up among 27 patients was 9 months. Four patients developed recurrence, four developed metastasis, and six (22.2%) died of disease. T4 stage and nodal disease correlated with higher disease-specific mortality. PCDFM arises in long-standing CD, usually presents symptomatically with abnormal anorectal imaging, and most often manifests as adenocarcinoma. Outcomes are stage dependent, underscoring the need for early recognition and multidisciplinary management.