EPD503 - Anal Adenocarcinoma in Inflammatory Bowel Disease: Clinicopathological Features and Association with Fistula Formation

Purpose/Background: Anal adenocarcinoma (AAC) is an uncommon malignancy, representing only 5-16% of anal cancers, but occurs with increased frequency among patients with inflammatory bowel disease (IBD). Chronic inflammation, persistent fistulae, and delayed diagnosis contribute to the elevated oncologic risk, yet standardized surveillance protocols are lacking. This study aimed to characterize the clinicopathological features, management strategies, and outcomes of IBD-associated AAC over a 21-year period, comparing fistula- and non-fistula-associated cases.

Methods/Interventions: A retrospective cohort study was conducted including all patients diagnosed with anal adenocarcinoma in the context of IBD between January 1, 2003, and December 31, 2024. Clinical records were reviewed for demographic characteristics, IBD subtype, association with perianal fistulae, tumor features (location, size, stage, histology), treatment modality, and recurrence.

Results/Outcomes: A total of 29 patients with IBD-associated anal adenocarcinoma were identified. The median age at cancer diagnosis was 58.5 years (IQR 47.5-63.3), and 65.5% were male. Median BMI was 25.3 kg/m² (IQR 22.8-28). Crohn's disease was present in 65.5% of patients and Ulcerative Colitis in 34.5%, the median IBD disease duration until cancer diagnosis was 30 (IQR 24 - 39.5) years. Fistula-associated adenocarcinoma occurred in 15 patients (51.7%). Tumor staging revealed 44.8% stage I-II and 37.9% stage III-IV disease. Median tumor size was 4.6 cm (IQR 3-6.8). Mucinous histology was observed in 20 patients (69.0%). Overall, 21 patients (72.4%) underwent surgical management, all receiving a curative abdominoperineal resection (APR), and six (20.7%) required concurrent pouch excision. Neoadjuvant chemoradiotherapy (CRT) was administered in 11 patients (37.9%), CRT alone in 6 (20.7%), and adjuvant therapy (chemotherapy and/or radiotherapy) in 15 (51.7%) patients. Tumors were larger in the fistula group (median 6.0 vs. 4.3 cm), although this difference did not reach statistical significance (p = 0.084). No significant differences were observed in pathological differentiation (p = 0.667) or AJCC tumor stage (p = 0.846). Recurrence occurred in seven patients (24.1%), including four cases of local recurrence, two of which were associated with a fistula. The estimated 3-year overall survival (OS) was 73.2% (95% CI 56.7-94.6) , while 3-year recurrence-free survival (RFS) was 75.6% (95% CI 60.3-94.8).

Conclusion/Discussion: IBD-associated anal adenocarcinoma is a rare but aggressive malignancy, with a higher incidence in patients with IBD and long-standing perianal disease. Although results were not statistically significant, likely due to small sample size, tumor size appeared larger in the fistula group, suggesting delayed recognition in chronic perianal disease. Early recognition of suspicious perianal changes and proactive surveillance protocols for chronic perianal IBD may enable earlier detection and improve outcomes in this high-risk population.

Table 1. Patient demographics, baseline characteristics, and tumor features
Figures represent median (IQR) or frequency (proportion)

*Some patients received more than one treatment agent

**One patient had both local and distant recurrence

BMI, Body mass index; IBD, Inflammatory bowel disease
Table 2. Tumor and treatment characteristics, oncologic outcomes
Figure represents median (IQR) or frequency (proportion)

*One patient had local and distant recurrence

RFS, Recurrence free survival; OS, Overall survival