Mammary hamartoma: immunohistochemical study of two adenolipomas and one variant with cartilage, smooth muscle and myoepithelial proliferation.

Three cases of mammary hamartoma were investigated immunohistochemically and are described. Case 1 was a 42 year old woman with an elastic hard tumor, 1.5 cm in diameter, in her left breast. Case 2 was a 49 year old woman with a semisoft tumor, 5 x 2 cm, in her right breast. Case 3 was a 47 year old woman with a hard tumor, 5 cm in diameter, in her left breast. In each case, mammography and ultrasonography revealed a benign-looking, well-circumscribed mass without calcification. Histologically, the tumors were composed of adipose tissue, mammary glands, and fibrous and/or fibromuscular tissue. The tumor in case 3 also contained small islands of hyaline cartilage. Immunohistochemical analysis was performed, and epithelial and mesenchymal components were discretely and differentially immunostained except that the smooth muscle component seemed to be derived from myoepithelial cells. Cartilage formation might be the result of metaplasia, and 'metaplastic variant of the mammary hamartoma' or 'choristoma' may be an appropriate term for cartilage-containing mammary hamartoma. Using proliferating cell nuclear antigen (PCNA)-immunostaining, we observed that each component of the tumors had an individual growth rate. This finding may reflect one aspect of the biological characteristics of hamartoma.