Abstract
A 53-year-old woman was scheduled for colonoscopy to investigate chronic diarrhea, but developed ileus in the pre-treatment period. Stenosis due to a full-circumference submucosal tumor-like lesion was observed in the rectosigmoid colon on colonoscopy performed at a later date. A biopsy showed no malignant findings. CT showed signs of wall thickening in the upper rectum. No lymph node metastasis or metastasis to other organs was observed, and she underwent laparoscopic lower anterior resection and colostomy of the transverse colon. Pathological diagnosis revealed well-differentiated tubular adenocarcinoma from the submucosal layer to the subserosal layer, with CK7-positive and CK-20-negative immunostaining. As this represented atypical colorectal cancer, postoperative chemotherapy was considered for cancer of unknown primary, but the patient did not consent and was therefore placed under follow-up observation. No recurrence or metastases were observed for 2 years and 4 months, and the colostomy was closed. We report our experience with a case of colorectal cancer requiring differentiation from cancer of unknown primary and presenting with a macroscopically and histologically specific appearance, and discuss with reference to the literature.
