This is a slowly growing lesion which occurs at all ages after puberty.
This lesion is microscopically indistinguishable from fibrocystic disease. The only distinction is the presence of compressed normal breast tissue at the margins of the lesion. There are rare reports of carcinoma, either in-situ or invasive, within a hamartoma of the breast.
Anani PA, Hessler CH. Breast hamartoma with invasive ductal carcinoma. Report of two cases and review of the literature. Pathol Res Pract 1996;192:1187-94.