Breast metastases from colorectal carcinoma

A case history is presented of a 53-year-old woman with an incidental finding of a breast lump, identified after having had chemotherapy for lung metastases from a rectal carcinoma. Clinical examination, ultrasound, mammography, fine needle aspiration and core biopsies could not prove definitively whether the breast lump represented a metastasis from colorectal carcinoma. Following local excision, the final diagnosis of metastatic colorectal carcinoma to the breast was based on the absence of any site of origin within the breast (i.e. no surrounding DCIS) and on the expression of cytokeratin CK7 and CK20 on immunohistochemistry. Postoperative chemotherapy was initiated. Four months later, although without local recurrence in the breast, the patient developed cutaneous metastatic deposits and active treatment was stopped. A review of other cases of breast metastases from extramammary sources is presented. Possible mechanisms for this rare and unusual phenomenon are discussed.