A case of anorectal malignant melanoma appearing 1 year after endoscopic mucosal resection of a rectal adenocarcinoma]

We present a case of a 61-year-old woman who underwent endoscopic mucosal resection (EMR) for early-stage colorectal cancer. However, because the condition of the horizontal margin of the resected tumor was unknown, she further underwent local transanal excision. Lower gastrointestinal endoscopy performed 1 year later showed protruding lesions both on the scar tissue and in the vicinity. Biopsy revealed malignant melanoma. She then underwent laparoscopic abdominoperineal resection and colostomy. This was an extremely rare case of adenocarcinoma complicated by malignant melanoma after resection.