Extramedullary hematopoiesis in breast after neoadjuvant chemotherapy for breast carcinoma.

We report incidental extramedullary hematopoiesis (EMH) in breasts of 2 patients following neoadjuvant chemotherapy for locally advanced breast cancer. Neither of the patients had a history of hematologic disorders. After chemotherapy, one of the patients had a complete pathologic response and the other had residual carcinoma. In both cases, EMH was mostly seen as myelopoiesis in a background of chemotherapy-induced changes. In the patient with residual carcinoma, EMH was observed in the contralateral prophylactic mastectomy specimen. EMH should be considered a diagnostic pitfall in the differential diagnosis of unusual cellular infiltrates in breast after neoadjuvant chemotherapy. To our knowledge, the association of EMH and neoadjuvant chemotherapy has not been previously reported.