CD10 and HHF35 actin in the differential diagnosis between Collagenous spherulosis and adenoid-cystic carcinoma of the breast.

Collagenous Spherulosis (CS) and Adenoid-Cystic Carcinoma (AdCC) of the breast consist of cribriform proliferations of epithelial and myoepithelial cells with an immunophenotypic overlap of some myoepithelial markers, such as p63 and smooth muscle actin (SMA). To our knowledge, CD10 and HHF35 actin have not been assessed in the differential diagnosis of these two breast lesions. We performed an immunohistochemical study on 6 cases of CS and 9 cases of AdCC. We found CD10, muscle-specific actin (HHF35), Estrogen and Progesterone receptors (ER and PR) to be strongly expressed in CS, but not in AdCC; C-kit was diffusely positive in AdCC and scanty in CS; SMA, p63 and Cytokeratine 5/6 (CK5/6) were positive in both. Our results also confirm that AdCC could be true basal-like neoplasia, probably arising from a basal stem line tending to divergent differentiation toward CK5/6/C-kit+, ER/PR-, epithelial basal-like cell type, and toward a myoepitelial-like cell type, with an incomplete SMA/p63+, CD10/HHF35- immunophenotype. By contrast, CS is a reactive, benign proliferation of two well-differentiated cell types: epithelial (ER/PR+, C-kit-) and myoepithelial cells with a complete immunophenotype including CD10/HHF35 positivity. Our study highlights the usefulness of CD10 and HHF35 in the differential diagnosis and helps to understand the histogenesis of the two lesions.