Spindle cell metaplastic carcinoma of breast: A clinicopathological and immunohistochemical analysis

To better characterize spindle cell metaplastic carcinoma (SpCMC) of breast, a rare variant of breast cancer that has been classified under the broad rubric of metaplastic carcinoma.

We presented herein 19 cases of metaplastic breast carcinoma with dominant spindle cell component. All cases were clinically of breast origin, showed more than 80% spindle morphology, 10 cases exhibited pure spindled morphology, 8 contained invasive ductal carcinoma (IDC) and 1 presented with ductal carcinoma in situ elements.

Immunohistochemical studies showed evidence suggesting myoepithelial and epithelial differentiation as exhibited by immunoreactivity for at least one myoepithelial and epithelial markers in all pure spindle cell components. IDC group showed 21.7% of axillary lymph nodes metastasis rate, whereas the axillary lymph node metastasis rate of the SpCMC group was 1.3%, significantly lower than that of the IDC group (P < 0.001). Immunohistochemical staining of IDC exhibited higher degrees of positivity for ER, PR and Her2 (90, 60 and 30%, respectively) when compared with the SpCMC group, which showed a positive degree of 5.2, 5.2 and 10.5% for ER, PR and Her2, respectively (P < 0.001).

Based on this series, SpCMC is a rare variant of metaplastic breast carcinoma with the distinct histopathological and immunohistochemical features. The biological behaviors of SpCMC, like axillary lymph node status, were quite different from that of IDC, suggesting that it may act as an independent pathologic subtype. Immunohistochemical analysis of a panel of epithelial and myoepithelial markers could contribute to the pathologic diagnosis of SpCMC.