Primary giant cell tumor of the female breast: a diagnostic red herring with therapeutic implications.

Primary giant cell tumor of the female breast is extremely rare. Major diagnostic difficulty is encountered not only by the surgeon but also by the radiologist and pathologist. Pathologically, it is similar to the bone and soft tissue counterparts. However, this is not always true. We describe a patient presenting clinically as cystosarcoma phyllodes and histopathological examination revealed a primary giant cell tumor which was confirmed by immunohistochemistry and electron microscopy. Interestingly, an intimate relationship between the mononuclear component of the tumor cells with eosinophils and mast cells was observed electron microscopically.