Hidden Metachronous Invasive Rectal Cancer after Repeated Endoscopic Treatment Following Ileorectal Anastomosis for Familial Adenomatous Polyposis: A Case Report.

introductionPatients with familial adenomatous polyposis (FAP) who undergo colectomy with ileorectal anastomosis (IRA) are at risk of adenoma recurrence and malignant transformation in the residual rectum. Advances in endoscopic techniques have enabled intensive surveillance with aggressive polypectomy to reduce the short-term risk of malignant progression. However, long-term management often requires a balance between endoscopic management and timely surgical intervention, and evidence to guide this balance remains limited. CASE PRESENTATION: A 54-year-old woman with FAP underwent total colectomy with IRA. During surveillance, an intramucosal rectal adenocarcinoma was detected at 65 years of age and resected transanally. Despite regular endoscopic treatment of recurrent lesions using endoscopic mucosal resection and argon plasma coagulation, the patient developed anal pain at 73 years of age. Imaging revealed a fluid collection suggestive of a posterior rectal wall abscess. Abdominoperineal resection was performed, and histopathological examination revealed invasive mucinous adenocarcinoma, leading to a diagnosis of metachronous rectal cancer. The patient has remained recurrence-free for 12 years postoperatively.

conclusionsThis case highlights the limitations of long-term endoscopic therapy in patients with FAP following IRA. Repeated interventions may have contributed to chronic inflammation and mucosal alterations, which might have impaired visualization and complicated the detection of invasive carcinoma. Clinicians should avoid relying solely on endoscopic management and should regularly reassess the need for timely surgical intervention.