Metastatic neoplasms of the breast: fine-needle aspiration cytology of two cases.

Even when clinical data strongly suggest the presence of a metastatic neoplasm in the breast, this occurrence almost invariably raises great problems in diagnostic pathology. Both cases presented here had a well-recognized primitive neoplasm located elsewhere. Nonetheless, great importance was given to the application of ancillary techniques; the immunostains for "breast discriminants"--GCDFP15, HMFG1, and HMFG2--on tissue sections helped the recognition of a metastatic renal cell carcinoma; and the stains for S100 protein, smooth muscle actin, cytokeratins, and neurofilaments on cytologic material allowed the identification of a metastatic mediastinal leiomyosarcoma.