Lymph node extramedullary hematopoiesis in breast cancer patients receiving neoadjuvant therapy: a potential diagnostic pitfall.

Extramedullary hematopoiesis (EMH) develops as a compensatory mechanism associated with hematologic processes but it may occur in association with chemotherapy. Three cases of EMH arising in axillary lymph nodes following neoadjuvant therapy for breast carcinoma are reported herein. Three women ranging in age from 41 to 47 years presented with unilateral breast masses measuring 0.6 to 4.0 cm in greatest dimension and were diagnosed with infiltrating ductal carcinoma, grade III by core needle biopsies. Two of the tumors were triple negative and one was estrogen receptor positive. All patients subsequently received neoadjuvant therapy followed by lumpectomies. No residual carcinoma was identified in postchemotherapy breast resection specimens. One patient underwent a sentinel lymph node procedure, the second patient an axillary lymph node dissection, and the third patient had a core biopsy of an enlarged axillary lymph node. The patient that underwent axillary lymph node dissection had metastatic carcinoma in one of her lymph nodes. Foci of EMH consisting of myeloid, erythroid, and megakaryocytic precursors were present within the nodal parenchyma and/or subcapsular sinuses of axillary lymph nodes of all three cases. Megakaryocytes were immunoreactive with factor VIII, erythroid elements with Glycophorin and myeloid precursors with myeloperoxidase. With increasing use of neoadjuvant therapy for breast carcinoma, EMH within lymph nodes is more likely to be encountered. Hematopoietic precursors present in lymph nodes may potentially be misdiagnosed as metastatic tumor cells, particularly as lobular carcinoma or metaplastic carcinoma. Therefore, caution should be exercised when evaluating axillary lymph nodes in the clinical setting of neoadjuvant therapy for breast carcinoma.