Carcinomas with metaplasia and sarcomas of the breast

The clinicopathologic, immunohistochemical, and flow cytometric characteristics of 34 cases of mammary carcinoma with metaplasia were compared with those of 20 cases of pure sarcoma of the breast. All 20 of the latter tumors showed the pattern of malignant fibrous histiocytoma. There were 20 cases of carcinoma with mesenchymal metaplasia, 7 cases of carcinoma with mixed epithelial (squamous) and mesenchymal metaplasia, and 7 cases of carcinoma with epithelial metaplasia (four mixed ductal/squamous and three pure squamous cell carcinomas). No patient with pure sarcoma had lymph node metastases develop; all nodal metastases were found in patients who had carcinoma with metaplasia, although in one case the carcinomatous component was seen only within a lymph node metastasis. Epithelial antigens were found not only within the epithelial elements of all cases of carcinoma, but also within the apparent mesenchymal elements of 44% of the carcinomas showing divergent differentiation. Flow cytometric analysis of eight cases of carcinoma with mesenchymal metaplasia showed aneuploidy/tetraploidy in six neoplasms. For patient management purposes, the distinction of pure sarcoma from carcinoma with metaplasia is important, but additional subclassification of carcinoma with metaplasia is of greater biologic than clinical interest.