Microinvasive lobular carcinoma associated with intraductal spread arising in a mammary hamartoma

A 53 year old woman presented with a lump in the inner lower quadrant of the left breast. Histological examination of the breast tumour confirmed that the lesion was a mammary hamartoma. Carcinoma with foci of microinvasion was observed in the lobules of the hamartoma concomitant with the intraductal spread of lobular carcinoma. Immunohistochemically, the cancer cells were negative for beta-catenin, which generally stained normal breast ducts and ductal carcinomas. This is only the sixth case of breast carcinoma arising in a mammary hamartoma to be reported and, moreover, the fourth case of lobular carcinoma occurring within a hamartoma. Despite the apparent rarity of this case, pathologists should be aware of the possibility of carcinomas arising within mammary hamartomas.