Background: Rosai-Dorfman disease (RDD), or sinus histiocytosis with massive lymphadenopathy, is a benign, self-limiting disease. In the majority of cases, there is massive and painless lymphadenopathy in any lymph node group but most commonly in the cervical lymph nodes, associated with constitutional symptoms. Extranodal involvement has been reported to occur in almost every organ system, with or without concomitant nodal disease. The breast is a rare site of presentation of this disease.
Case: A 35-year-old male presented with a hard, nodular swelling in the lower and outer quadrant of the right breast, with a clinical suspicion of malignancy. A diagnosis of sinus histiocytosis with massive lymphadenopathy, or RDD, was offered based on the presence of numerous lymphocytes, plasma cells, a few neutrophils and large histiocytes showing emperipolesis in fine needle aspiration smears.
Conclusion: Mammary RDD is extremely rare in males. The cytologic features are fairly characteristic and should be considered in the differential diagnosis whenever atypical histiocytes and emperipolesis are encountered in fine needle aspiration smears.