Primary plasmacytoma of the breast.

We describe a solitary extramedullary plasmacytoma of the breast in a 37-year-old woman. No other involvement was detected in the bone marrow or in any other site during a 15-month follow-up period. Extramedullary plasmacytomas of the breast are extremely rare, especially those that are not associated with multiple myeloma. We review the histologic features of the previously reported cases with an emphasis on differential diagnosis and the difficulties encountered in arriving at the correct diagnosis in frozen sections.