Pleomorphic carcinoma with osteoclastic giant cells of the breast: immunohistochemical differentiation between coexisting neoplastic and reactive giant cells.

Herein is described a unique case of breast carcinoma with two different types of giant cells noted in both cytological and histological specimens. A 51-year-old Japanese woman noticed a hard mass in the upper outer quadrant of her left breast. Aspiration cytology exhibited numerous anaplastic giant cells; the cytological diagnosis was high-grade ductal carcinoma, although a few osteoclastic giant cells were also observed. A left simple mastectomy and sentinel lymph node biopsy were performed. Histologically, approximately 90% of the tumor was composed of giant cells; conventional invasive ductal carcinoma and ductal carcinoma in situ were found focally at the periphery of the tumor. The main part of the tumor contained both anaplastic, neoplastic giant cells and non-neoplastic, osteoclastic giant cells that were distinguishable from nuclear atypism. The presence of the two types of giant cells was also confirmed on immunohistochemistry using a histiocytic marker (CD68) and two epithelial markers (AE1/AE3 and CAM5.2). Based on the latest World Health Organization classification, the diagnosis was pleomorphic carcinoma with osteoclastic giant cells. To the authors' knowledge there has been no previous report on this subject except for a single case mentioned in Rosen's Breast Pathology.