Malacoplakia and Rosai-Dorfman disease: two entities of histiocytic origin infrequently localized in the female breast--the cytologic aspect in aspirates obtained via fine-needle aspiration cytology.

We describe one case of Rosai-Dorfman disease (RDD) localized in the breast and one case of breast malacoplakia (MPK) both diagnosed by fine-needle aspiration cytology (FNAC). In RDD the cytologic features were lymphocytophagocytosis, large histiocytes with slight nuclear atypia, and lymphohistiocytic aggregates in a polymorphous background which included frequent plasma cells. In MPK the key diagnostic feature was the presence of Michaelis-Gutmann bodies (M-G bodies), in various stages of evolution, intermingled with vacuolized medium-sized histiocytes, other inflammatory cells, and debris. Pap staining is the technique of choice to show lymphocytophagocytosis and M-G bodies and there is no need to resort to special staining methods. RDD and MPK share a common cytologic background: the presence of numerous benign reactive histiocytes, either engulfing apparently intact lymphocytes, or phagocytizing M-G bodies. The cytologic findings seen in both cases suggest that the presence of histiocytes in a breast aspirate is far from being nonspecific and can represent an important lead to disparate diseases such as RDD and MPK.