A Surprising Diagnosis in a Breast Lump: The First Case Report of Uterine Carcinosarcoma Presenting as Breast – Only Metastasis

Extra-mammary breast malignancies are rarely the source of a metastatic breast mass. Uterine carcinosarcoma (UCS) is a rare disease with aggressive features and poor survival due to late presentation and advanced stage at diagnosis. Peritoneal seeding and cancer dissemination are not uncommon, but metastasis to the breast is extremely rare. Here we report a case of metastatic carcinosarcoma of uterus with unusual presentation as a breast lump without gynecological symptoms. Tissue biopsy and immunostaining confirmed the diagnosis. Few cases have been reported in the literature, mainly of serous type with the development of metastatic disease at multiple sites. To date, this is the only reported case of uterine carcinosarcoma metastasizing to the breast only, without intrabdominal dissemination, peritoneal carcinomatosis or another distant metastasis. We discuss presentation, diagnosis, methods of differentiation, and the up-to date treatment recommendations.