Rosai-Dorfman disease of the breast mimicking cancer.

Rosai-Dorfman disease or sinus histiocytosis with massive lymphadenopathy is a rare proliferative histiocytic disorder of the lymph nodes. Extranodal involvement occurs in a considerable number of cases; however, involvement of the breast is very rare, and it is even rarer for the lesion to be localized in the breast alone without affecting any other sites. This report describes the case of a 50-year-old Brazilian woman with a lump confined to her left breast that had clinical and radiological characteristics indistinguishable from cancer.