Context.—A micropapillary carcinoma (MC) component is generally considered to behave aggressively. Although several reports have described the prognostic significance of MC in breast carcinomas, immunohistochemical findings of MC, especially as compared to non-MC, are rarely described.

Objective.—We compared clinicopathologic and immunohistochemical findings between 38 cases of invasive breast carcinoma with an MC component (IMC) and 217 cases of invasive breast carcinoma without an MC component (NIMC).

Design.—We constructed a tissue microarray from 38 cases of IMC and performed immunohistochemical stainings for cytokeratin (CK) 7, CK20, estrogen receptor, progesterone receptor, p53, c-Erb-B2, CD34, CK5, epidermal growth factor receptor, and c-Kit in both MC and non-MC components.

Results.—Cases with IMC were associated with greater tumor size, more frequent lymphovascular invasion, nodal metastases, greater mean numbers of positive lymph nodes, and higher stage than those with NIMC, but were not associated with poorer survival rates. On immunohistochemistry, only p53 reactivity was statistically different between MC and non-MC components in IMC cases. Estrogen receptor positivity tended to be lower in MC than non-MC, but the difference was not significant. Most of the MCs and non-MCs in IMC cases were positive for CK7, but none of them were positive for CK20, CK5, epidermal growth factor receptor, or c-Kit.

Conclusions.—Based on the frequent nodal metastases and association with higher stage found in IMC as compared with NIMC cases, as well as higher p53 positivity and lower frequency of estrogen receptor expression, MC could be considered an aggressive histologic type of breast carcinoma. In both MC and non-MC components in IMC cases, no basallike immunostaining pattern was detected.