Pedunculated polyp of early sigmoid colon cancer with invasive micropapillary carcinoma.

A 64-year-old man was admitted to Dongo Hospital (Nara, Japan) with colonic cancer, following the onset of abdominal pain, diarrhea and fever. A pedunculated polyp was detected in the sigmoid colon by colonoscopy, and laparoscopy-assisted sigmoidectomy with regional lymph node resection was performed. Histopathologically, the tumor exhibited massive invasion of the submucosa, and multiple lymph node metastases were detected. The tumor mainly consisted of a micropapillary component. Immunohistochemically, MUC1 was expressed at the stromal edge of the micropapillary component and showed the characteristic 'inside-out' pattern of a micropapillary carcinoma. The multiple lymph node metastases were predominantly composed of carcinoma with a micropapillary pattern. Our case suggests that when a micropapillary component is identified in a pre-operative biopsy specimen, even for a pedunculated early colorectal cancer, the extent of surgical resection should be carefully considered due to the high potential for nodal metastasis.