Clinicopathological study of a dimorphic variant of breast carcinoma.

Background: Dimorphic cells have abundant clear cytoplasm similar to myoepithelial cells, and the nuclei are identical to those in adjacent malignant columnar epithelial cells. A dimorphic variant of a breast carcinoma involves a neoplastic proliferation of epithelial cells including dimorphic cells.

Methods: The subjects were patients with primary breast carcinoma, who underwent surgical resection at the Hospital of Dokkyo Medical University between 2000 and 2016, and were reviewed and diagnosed with a dimorphic variant of breast carcinoma.

Results: Dimorphic ICs typically showed a low-grade tumor and Hormonal receptor (HR) (estrogen and/or progesterone)+/HER2- subtype. Age, mean tumor size, status of nodal metastasis, stage and disease-free survival and overall survival did not differ between dimorphic and non-dimorphic ICs. The dimorphic cells were negative for p63 and cytokeratin 5/6 and 14 in most cases. In contrast, dimorphic cells were positive for HR, androgen receptor, and showed marked membrane-associated staining for E-cadherin and cytoplasmic staining for gross cystic disease fluid protein 15.

Conclusions: The morphological features of dimorphic cells may be confused with cells of other origins if the features of the dimorphic cells are not recognized. However, the typical morphological architecture of this carcinoma and expression of immunohistochemical markers support the diagnosis.