Fine-needle aspiration cytology of mesenchymal tumors of the breast.

This report describes the fine-needle aspiration (FNA) cytologic findings of 15 cases of sarcomas involving the breast out of a combined series of 2,064 breast FNA biopsies, including 580 malignancies, thereby accounting for 2.6% of all the malignant breast tumors. The series consisted of 14 women and one man with a mean age of 48.4 yr (range, 29-63). There were eight cases of cystosarcoma phyllodes, including one malignant cystosarcoma phyllodes. Three benign cystosarcoma phyllodes had a significant concomitant atypical epithelial hyperplasia, which lead to a misdiagnosis of carcinoma in two of the cases. The third case was correctly identified as recurrent cystosarcoma phyllodes. In retrospect, features suggestive for cystosarcoma phyllodes and unusual for breast carcinoma include increased numbers of naked nuclei and hypercellular stromal fragments. Sarcomatous patterns in our four metaplastic carcinomas included chondrosarcoma (two cases), malignant fibrous histiocytoma (MFH) (one case), and fibrosarcoma (one case). Two additional pure primary MFHs (both of which had electron microscopic confirmation) and one metastatic fibrosarcoma to the breast were encountered. Recognition of unusual cytologic patterns for breast carcinoma should suggest the possibility of a primary or metastatic sarcoma to the breast. Potential pitfalls for misdiagnosis include the presence of atypical epithelial hyperplasia in some cases of cystosarcoma phyllodes, along with occasional cases having patterns indistinguishable from a fibroadenoma. The pleomorphic and bizarre cellular features can suggest the diagnosis of metaplastic and pure sarcomas of the breast, although the potential exists for confusion with very poorly differentiated carcinoma. FNA diagnosis of sarcomatous lesions of the breast is essential in order to insure proper surgical treatment.