Microglandular adenosis of the breast. An immunohistochemical comparison with tubular carcinoma.

Microglandular adenosis (MA) of the breast is a benign, disorganized proliferation of glands lined by a single layer of cells. As such, differential diagnosis between MA and tubular carcinoma may be challenging in selected cases. A panel of antibodies was applied to 10 cases of MA and 10 of tubular carcinoma to investigate the potential benefit of immunohistochemistry in the separation of these lesions and the possible role of myoepithelial cells in MA. The luminal cells in nine cases of MA were surrounded by a cuff of muscle-specific actin-reactive cells, which also coexpressed cytokeratin and vimentin. The immunophenotype of these cells is characteristic of myoepithelial differentiation, which was heretofore thought to be lacking in MA. This finding demonstrates that myoepithelial cells are indeed present in MA subjacent to luminal epithelial cells; moreover, it distinghuishes MA from tubular carcinoma, all examples of which were actin negative in this analysis. In addition, circumferential type IV collagen deposition was observed around constituent glands of MA in nine cases but was lacking in all tubular carcinomas. Other markers included in this evaluation (S100 protein, gross cystic disease fluid protein 15, carcinoembryonic antigen, estrogen receptor protein) were of no differential diagnostic value.