Mammary Rosai-Dorfman disease: Rare benign mimic of breast malignant neoplasm.

Rosai-Dorfman disease (RDD), also known as sinus histiocytosis with massive lymphadenopathy, is an uncommon benign disorder characterized by the accumulation of activated histiocytes in affected tissues. While RDD typically involves lymph nodes, it may manifest as extranodal involvement. Breast involvement is an exceedingly rare presentation of this condition with <100 reported cases worldwide. This report presents a case of RDD in a 58-year-old male patient who presented with a palpable breast mass. Mammography and ultrasound imaging studies raised concerns for malignancy, prompting a breast biopsy. Histopathological examination revealed S100-positive pale histiocytes exhibiting emperipolesis, consistent with RDD. The management of extranodal RDD is individualized, as no standardized guidelines are currently available. However, surgical excision is recommended for unicentric breast lesions, which was performed in our case, resulting in complete remission. The patient has remained disease-free under surveillance with computed tomography scans. Our case underscores the importance of considering RDD in the differential diagnoses of breast masses and highlights the utility of surgical excision as an effective treatment option, especially for unicentric breast lesions of RDD.