Small Bowel Adenocarcinoma Arising in Long-Standing Stricturing Crohn's Disease: Diagnostic Challenges and Therapeutic Dilemmas.

Small bowel adenocarcinoma (SBA) is a rare but severe complication of long-standing Crohn's disease (CD), particularly in patients with stricturing phenotypes. Its diagnosis is often delayed due to overlapping clinical and radiological features with inflammatory disease. We report the case of a 52-year-old man with an 18-year history of stricturing and fistulizing ileal CD, previously treated with azathioprine and adalimumab. Despite clinical remission, magnetic resonance enterography performed during therapeutic reassessment revealed complex stricturing disease with fistulizing features. Surgical resection was undertaken. Histopathological examination revealed mucinous adenocarcinoma with a signet-ring cell component exceeding 30%, staged as pT2N0 after complete (R0) resection. Postoperative management included close radiological surveillance without adjuvant chemotherapy. Given the recent cancer diagnosis, a temporary treatment-free strategy for CD was initially adopted, with monitoring of fecal calprotectin levels. Endoscopic recurrence led to the introduction of ustekinumab. At 12-month follow-up, the patient remains clinically stable with no evidence of oncological recurrence. This case highlights the diagnostic challenge of SBA in CD, particularly in clinically quiescent patients. It underscores the absence of validated screening strategies and emphasizes the importance of multidisciplinary decision-making in balancing oncologic safety and inflammatory disease control.