Recurrence of Transverse Colon Cancer in Diverticulum 14 Years after Endoscopic Mucosal Resection: A Case Report

Carcinoma arising from a colonic diverticulum is extremely rare, with only 21 cases being reported in the literature. Accurate pathological assessment of lesions within diverticula is often challenging due to distortion or discontinuity of the muscularis mucosae, which may lead to misjudgment of invasion depth and inappropriate therapeutic decisions.

We report the case of a 74-year-old female with a history of left breast cancer and prior endoscopic mucosal resection (EMR) for a 7-mm transverse colon cancer 14 years earlier. Histopathology at that time revealed a moderately differentiated adenocarcinoma with submucosal invasion of 800 μm, negative vertical and horizontal margins, and no indication for additional surgery. Surveillance colonoscopy at 6 months showed only a scar, but then she was lost to follow-up. After detection of an elevated carcinoembryonic antigen level of 56.8 ng/mL, the patient was referred to us. A lesion adjacent to the transverse colon was seen on CT and PET, but no abnormalities were seen on colonoscopy. We performed laparoscopic transverse colectomy with D2 lymph node dissection. Histopathological examination revealed a tumor centered in the subserosal/pericolic tissue, histologically identical to the prior EMR specimen, staged as pT3, and consistent with local recurrence of the original lesion. Re-evaluation of the original EMR slides with desmin immunostaining confirmed that the tumor had arisen within a diverticulum, and the true invasion depth was 4000 μm rather than the initially reported 800 μm. The patient recovered uneventfully, underwent laparoscopic incisional hernia repair 1 year later, and remains recurrence-free 24 months after colectomy.

This case highlights the diagnostic difficulty of accurately assessing invasion depth in tumors arising within diverticula. Misinterpretation may result in underestimation of metastatic risk and inadequate treatment. In this case, recurrence of colon cancer was detected 14 years after EMR. Diverticula should always be carefully documented during colonoscopy and should be considered in pathological interpretation. Recurrence may occur many years after endoscopic therapy, so close communication between endoscopists and pathologists is essential, and long-term surveillance is warranted.