Myoid hamartomas of the breast.

Tumors containing smooth muscle are rare in the breast. A myoepithelial origin for the myoid component of such lesions was postulated in previous reports. Myoepithelial hyperplasia has long been recognized as a common component of some breast lesions, including sclerosing adenosis, papillomas, and fibroadenomas. Three breast tumors composed of variable admixtures of adipose tissue, fibrous tissue, and smooth muscle are described. The authors postulate that the myoid component of two of the three lesions may have arisen in a milieu of myoepithelial hyperplasia. The origin of the myoid component in the third case is not clearly defined.