Intermediate-sized filament proteins (keratin, vimentin, desmin) in metaplastic carcinomas, carcinosarcomas and stromal sarcomas of the breast.

The distribution of intermediate-filament (IF) proteins of the keratin, vimentin and desmin type in breast stromal sarcomas, carcinosarcomas, metaplastic carcinomas and phyllodes tumors has been compared using the avidin-biotin complex immunoperoxidase technique. Keratin reactivity was found in carcinomatous and pseudosarcomatous areas of all metaplastic carcinomas, in the cuboidal epithelial cells of carcinosarcomas and in the epithelial component of phyllodes tumors. Vimentin and desmin were detected in the sarcomatous portion of carcinosarcoma, focally in the stromal component of phyllodes tumors and not always in the stromal sarcomas. These data confirm that combined analysis of IF expression is a reliable and convincing way to differentiate stromal sarcomas, metaplastic carcinomas and carcinosarcomas in breast pathology.