Immunohistochemical assessment of proliferative activity in mammary adenomyoepithelioma

Aims: Two cases of adenomyoepithelioma of the breast were examined by immunohistochemistry to evaluate proliferative activity of epithelial and myoepithelial components. Methods and results: The tumours showed a bicellular pattern of gland-forming epithelial cells and proliferative myoepithelial cells with clear cytoplasm, They showed foci of monotonous growth of myoepithelial cells devoid of glands with low mitotic rate (1 similar to 2/10 high-power fields) and mild cytological atypia. Immunohistochemically, the glandular cells were positive for epithelial membrane antigen, cytokeratin (KL-1 and CAM5.2) and carcinoembryonic antigen, whereas tumour cells with clear cytoplasm were reactive with muscle-specific actin (MSA), alpha smooth muscle actin, vimentin, and S100 protein but negative for desmin, Proliferative activities assessed by MIB-1 (Ki-67)/MSA positive cell index were greater in myoepithelial cells in both cases (19.2% and 17.7%) as compared to those in epithelial cells (MIB-1/CAM5.2 index: 10.2% and 9.5%). Conclusions: These results might account for the previous findings that myoepithelial components predominate over the epithelial ones in an advanced stage of this tumour as well as in recurrent or metastatic lesions.