Mammary hamartomas: An immunohistochemical study of ten cases

Ten cases of breast hamartomas were reviewed; the patients' age ranged from 31 to 55 (mean 40.4, median 39). All cases presented with a palpable, some times tender, lump. The typical mammographic feature was a well defined, ro und to lens shaped, variable dense mass, occasionally surrounded by a thin radiolucent zone. All hamartomas were unilateral (4 in the right and 6 in t he left breast, respectively) and no recurrence occurred after local excisi on. The tumor size ranged from 5 to 150 mm (mean 54 mm). Histologically all hamartomas were composed of a typical fibrous, adipose a nd glandular tissue combination. Immunohistochemically there was a strong p ositivity for cytokeratin and epithelial membrane antigen in the epithelial cells, a positive finding for vimentin and muscle-specific actin in stroma l and myoepithelial cells, and for S-100 protein in myoepithelial cells. Ve ssels endothelial cells were immunoreactive for Factor VIII. Immunohistochemical analysis of hormone receptors completed on formaldehyde -fixed paraffin-embedded specimens, showed estrogen and progesterone recept ors positivity in 9 cases and estrogen positive progesterone negative recep tors in one case. In all cases the receptorial positivity was limited to th e epithelial elements. These data revealed that 1) breast hamartoma is a benign, tumor-like lesion , histologically dissimilar from other lesions such as fibroadenoma and pse udoangiomatous hyperplasia; and 2) hamartoma tissue is influenced by hormon es like the surrounding normal breast parenchyma.