Carcinoma of the breast with multinucleated reactive stromal giant cells. A light and electron microscopic study of two cases.

Two unusual carcinomas of the breast are described, containing nests of infiltrating neoplasm situated within stromal lacunar spaces, and surrounded by numerous benign appearing multinucleated giant cells. Within the stroma, there was extensive hemorrhage, hemosiderin pigment deposition, and large numbers of mononucleated inflammatory cells. The morphology of both tumors resembled the giant cell tumor of bone. Although a similar giant cell reaction has recently been described in association with a uterine leiomyosarcoma, we are aware of only two other examples of this entity in the breast, both reported over 40 years ago in the French literature. This is the first report in which electron microscopy confirmed the benign histiocytic nature of the giant cells. These cells had many of the ultrastructural features of multinucleated giant cells described in tissue culture, skeletal osteoclastomas, and foreign body granulomas. We propose that the giant cells arise from fusion of mononucleated stromal cells, and most likely are reactive histiocytic elements which are in some way related to the tumor cell nests. Further studies of these unusual neoplasms are needed to determine if the giant cell reaction in any way affects the prognosis of the patient.