Rosai-Dorfman Disease: A Rare Case of Extranodal Breast Involvement

Rosai-Dorfman disease (RDD) is a rare histiocytosis most commonly found in cervical lymph nodes. Extranodal manifestations occur in a variety of tissues, of which the breast is an exceedingly rare location. The differential diagnosis may be narrowed with breast ultrasound, mammography, MRI, and FDG PET/CT, and definitive diagnosis is achieved through biopsy, with the hallmark histologic finding of emperipolesis. Although generally self-limiting, symptomatic lesions can be treated with surgical excision, with more favorable outcomes attained for unifocal disease compared with multifocal, disseminated disease. We report the case of a 32-year-old woman with progressive, multifocal RDD in the breast and subsequent discovery of an extranodal subcutaneous palpable thigh nodule likely representing an additional site of disease.