Primary osteogenic sarcoma and osteogenic metaplastic carcinoma of the breast. Immunocytochemical identification in fine needle aspirates.

Pleomorphic spindle cells, osteoclastlike giant cells and plaques of osteoidlike material were the cytologic features observed in fine needle aspirates of the breast tumors from two patients. This cytologic pattern suggested a diagnosis of osteogenic sarcoma, a rare neoplasm in the breast. Immunoperoxidase staining performed on the original smears showed reactivity for vimentin in both cases. One tumor was also positive for epithelial membrane antigen (EMA); reactivity for this marker revealed the metaplastic nature of the sarcomatous cells in this tumor, suggesting a diagnosis of metaplastic carcinoma. Histologically, both tumors showed a sarcomatous pattern, with osteoid and chondroid formation, with no evidence of epithelial differentiation. Polyclonal and monoclonal antibodies against epithelial and mesenchymal markers used in tissue sections confirmed the immunophenotypes identified cytologically. Based on the immunochemical findings, the final diagnoses were osteogenic sarcoma of the breast in one case and osteogenic metaplastic carcinoma of the breast in the second case. Both patients died of metastatic disease within one year. These cases (1) show the reliability and accuracy of the immunoperoxidase method in making a differential diagnosis of ambiguous cytologic patterns in fine needle aspirates, (2) support the occurrence of a true osteogenic sarcoma of the breast (comparable to its skeletal counterpart) and (3) demonstrate that metaplastic carcinomas may closely simulate sarcomas of the breast, morphologically as well as biologically. Immunochemical staining techniques play an important role in the differential diagnosis of these neoplasms.