Anastomosing Hemangioma of the Breast: An Unusual Case at an Unusual Site.

Anastomosing hemangioma (AH) is an unusual benign vascular lesion that commonly occurs in the kidney and genitourinary tract. We report a case of AH in a 49-year-old woman presenting as a mass in the breast, a site which, to the best of our knowledge, has not been previously documented in the English literature. Microscopic examination of the mass revealed a well-demarcated proliferation of anastomosing vascular spaces lined by bland endothelial cells, with focal hobnailing and scattered intravascular fibrin thrombi. No mitotic activity was observed and the Ki-67 proliferative index was low. These features were interpreted as AH, a lesion that may be difficult to distinguish from low-grade angiosarcoma or other benign vascular lesions of the breast which may demonstrate anastomosing channels. Due to the presence of atypical histologic features which can raise suspicion for angiosarcoma on biopsy, complete excision of these lesions is recommended for optimal treatment.