Rosai-Dorfman Disease in the breast with increased IgG4 expressing plasma cells: a case report.

Rosai-Dorfman disease (RDD) can present in any anatomic site, but breast involvement is rarely reported. Recently, a relationship between RDD and IgG4-related sclerosing disease has been suggested. Here we report another case of RDD with overlapping features of IgG4-related sclerosing disease occurring in a right breast of a 62-year-old female. On microscopic examination, the mass demonstrated a characteristic zonal pattern of proliferation of large polygonal histiocytes and lymphoplasma cells with stromal fibrosis. Emperipolesis was observed in histiocytes with abundant cytoplasm, which showed immunoreactivity for S-100 protein and CD68; the diagnosis of RDD was made. Sheets of plasma cells in the fibrotic stroma demonstrated positive reactions for IgG and IgG4. The mean count of IgG4-positive plasma cells was 100.2/high power field, and the ratio of IgG4/IgG was 56.7%. Additional findings of stromal fibrosis and obliteration of preexisting breast lobules suggested overlapping features with IgG4-related sclerosing disease.