The histological and immunohistochemical evidence of squamous metaplasia from the myoepithelial cells in the breast

Squamous metaplasia in the breast is well documented. However, the putative cell of origin for the squamous epithelium is not clear. This paper describes a case of fibroadenoma of the breast with myoepithelial hyperplasia and squamous metaplasia. The histological finding of transition between myoepithelial cells and squamous cells and the immunohistochemical expressions of actin and S-100 in the metaplastic squamous cells support the myoepithelial origin of squamous epithelium in the breast.