Rosai-Dorfman disease presenting as a male breast mass.

A 23-year-old man presented with a 6-week history of a left breast mass. Mammography and ultrasonography confirmed a 1.1 x 0.7-cm mass suggestive of breast cancer. An excisional biopsy revealed Rosai-Dorfman disease of the breast. As illustrated by this case, extranodal Rosai-Dorfman disease can mimic breast cancer. Surgical resection is considered appropriate treatment for this condition.