Combined Epithelial-Myoepithelial Lesions of the Breast

Epithelial-myoepithelial proliferations of the breast are a heterogeneous poorly defined group of lesions characterized morphologically by dual differentiation into ductal (luminal) and myoepithelial cells. They include neoplastic and non-neoplastic entities that have overlapping morphologic features that may give rise to diagnostic difficulty. Many of these entities are low grade or of uncertain malignant potential but the biology of some of these rare lesions remains to be elucidated. This article discusses the differential diagnosis of epithelial-myoepithelial lesions of the breast and highlights the morphologic features of some of these entities.