Rosai-Dorfman disease of the breast: a case report

Abstract

Abstract Rosai-Dorfman disease is a benign proliferative disorder of histiocytes that typically involves the cervical lymph nodes in children and young adults. Extranodal Rosai-Dorfman disease develops in a considerable number of patients; however, Rosai-Dorfman disease of the breast is rarely encountered and may mimic malignancy. We present a 57-year-old woman who was seen for a painless firm mass in the upper outer quadrant of her right breast. Biopsy of the mass showed granulomatous mastitis, and the patient underwent surgical excision subsequently. Gross examination revealed one poorly circumscribed, vaguely lobulated, and variegated mass measuring 3.8 x 3.8 x 2.6 cm. Histology was notable for a marked lymphohistiocytic infiltrate with no identifiable breast tissue. The histiocytes were large with round nuclei and voluminous cytoplasm and demonstrated emperipolesis. Immunohistochemical studies showed that the histiocytes expressed S100, and the lymphocytic infiltrate was composed of CD3-postive T cells and CD20-postive B cells. Also, staining for IgG and IgG4 highlighted plasma cells with IG4-positive ones comprising < 10% of the plasma cell population. The histiocytes did not express CD1a. Pancytokeratin stain was negative, and the Ki-67 proliferation index was low. These findings were most consistent with Rosai-Dorfman disease. As we illustrate in this case study, Rosai-Dorfman disease of the breast can present with a firm and painless mass, posing a diagnostic challenge clinically and radiologically. Therefore, it is crucial to establish the correct diagnosis to avoid aggressive surgical or chemotherapeutic treatment.