Unusual Tumor in an Unusual Localization: Sclerosing Extramedullary Hematopoietic Tumor in Breast With Literature Review

Background Sclerosing extramedullary hematopoietic tumor (SEMHT) is a rare entity that can occur in patients with myeloproliferative neoplasms. It has been reported in various localizations including retroperitoneum, mesentery, liver, colon, lymph nodes, thyroid, and orbit. It is considered as late manifestation of the underlying myeloid neoplasm. It is clinically important to distinguish from extramedullary hematopoiesis, as well as mesenchymal tumors. Presentation A 81-year-old female patient with a history of left breast ductal carcinoma in situ who underwent breast lumpectomy followed by radiation was diagnosed with polycythemia vera the following year. Two years later, two indistinct masses were incidentally identified in the patient's right breast. Breast biopsy showed effaced normal breast architecture, sclerotic/fibrotic background with scattered markedly atypical large cells with large, hyperchromatic nuclei. The immunohistochemical studies on the biopsy were inconclusive and diagnosis of atypical mesenchymal neoplasm with recommended resection was rendered. The resection specimen showed similar morphology. Immunohistochemistry stains were performed, CD61 and FVIII proved the large, atypical cells were atypical megakaryocytes. Glycophorin A stained the erythroid cells, and myeloperoxidase was positive in myeloid cells, identifying this as a SEMHT. Discussion : SEMHT is an uncommon tumor, exceptionally rare in breast. The main differential diagnoses include extramedullary hematopoiesis, metaplastic carcinoma of the breast, pseudo angiomatous stromal hyperplasia (PASH), fibroblastic/myofibroblastic tumors of the breast, mesenchymal tumors. Conclusion SEMHT is a rare entity that can present in any body sites. To recognize this entity in the breast tissue along patient's history to avoid diagnostic pitfall is essential for clinical guidance.