Invasive colorectal micropapillary carcinoma: an aggressive variant of adenocarcinoma.

Micropapillary carcinoma (MC) has been well described in other organs, including breast, urinary bladder, lung, ovary, and salivary gland, but has not been described in the large intestine. We compared the clinicopathologic and immunohistochemical findings of MC with those of conventional adenocarcinoma in the large intestine. Fifty-five cases of adenocarcinoma with an MC component were identified among 585 consecutive cases of colorectal cancer at the Asan Medical Center between January 2003 and June 2004 and were compared with 119 cases of conventional adenocarcinoma of colorectum without an MC component. Arrayed tissue blocks were constructed and immunostained for cytokeratin 7 and 20 and CDX2. We also compared the results of MLH-1, MSH-2, p53, and carcinoembryonic antigen immunostainings between the 2 groups. The grade of both MC and conventional adenocarcinoma was mostly moderately differentiated. The proportion of MC ranged from 5% to 80%. The presence but not extent of MC in the primary tumors was associated with more frequent lymphovascular invasion and lymph node (LN) metastases, a greater mean number of positive LNs, and a higher tumor stage with more frequent distant metastases, compared with conventional adenocarcinoma (P < .05). Cytokeratin 7 staining was occasionally observed in both MC (9.1%, 5/55 cases) and conventional adenocarcinoma (13.4%, 16/119 cases). Although MLH-1 and CDX2 expression tended to be lower in conventional adenocarcinoma, none of the immunohistochemical results was significantly different between 2 groups. Recognition of MC component is important as MC appeared to be an aggressive variant of colonic adenocarcinoma and presented at a higher stage, with frequent lymphovascular invasion, LN metastasis, and distant metastasis, compared with conventional adenocarcinoma. The proportion of MC component did not impact the prognosis, and the immunoprofiles of MC were not significantly different from those of conventional adenocarcinoma.