Invasive micropapillary carcinoma of the colon: an immunohistochemical study.

Invasive micropapillary carcinoma has recently been reported in various anatomic sites. In this article, we report a case of micropapillary carcinoma of the sigmoid colon. A 70-year-old Japanese woman presented with bloody stool for 2 months. Detailed examination disclosed ulcerative and localized tumor in the sigmoid colon. Histological examination of the colon tumor showed a combination of conventional adenocarcinoma (60%) and micropapillary carcinoma (40%). Immunohistochemically, micropapillary carcinoma cells were positive for cytokeratin (CK) 20, carcinoembryonic antigen, and CA125, but negative for CK7, thyroid transcription factor-1, surfactant apoprotein A, estrogen receptor, and progesterone receptor. Additionally, the immunohistochemistry of epithelial membrane antigen revealed reverse polarity of neoplastic cells. Results of conventional adenocarcinoma were basically identical to those of micropapillary carcinoma. In the stroma of both conventional adenocarcinoma and micropapillary carcinoma, many myofibroblasts were present and CD34-positive stromal cells were absent. Finally, we report the fourth case of micropapillary carcinoma arising in the colon. Immunohistochemical results of CK7(-)/CK20(+) strongly suggest the colon as a primary site of micropapillary carcinoma. Additionally, micropapillary carcinoma of the colon may cause a similar stromal reaction to conventional adenocarcinoma of the colon.