Isolated bilateral breast myeloid sarcoma: A rare case report.

Myeloid sarcoma (MS) is a rare extramedullary tumor composed of immature myeloid cells that is most associated with acute myeloid leukemia (AML), whereas isolated bilateral breast involvement without bone marrow disease is exceptionally uncommon. We report the case of a 38-year-old woman who presented with bilateral breast masses, both classified as BI-RADS 5 on imaging. Ultrasound-guided core needle biopsies of both breast lesions established the diagnosis of myeloid sarcoma, with immunohistochemical positivity for MPO, CD34, CD56, and CD117. Peripheral blood and bone marrow examinations showed no evidence of AML, and FDG PET/CT confirmed isolated extramedullary disease, providing accurate staging and monitoring treatment response. The patient received AML-type induction chemotherapy followed by salvage FLAG-IDA chemotherapy for residual disease and consolidative radiotherapy, achieving complete metabolic remission that was maintained at 6-month follow-up. This case highlights the diagnostic challenges of isolated bilateral breast myeloid sarcoma and emphasizes that histopathological confirmation with immunohistochemistry, complemented by FDG PET/CT, is important for accurate diagnosis, staging, treatment assessment, and multidisciplinary management.