Breast relapse of myeloid sarcoma and SARS-CoV-2 infection following hematopoietic stem cell transplantation in mixed-phenotype acute leukemia: a case report

Abstract Background Mixed-phenotype acute leukemia is a rare, high-risk subtype of acute leukemia. Myeloid sarcoma is a localized tumor formed by the proliferation and infiltration of primitive or immature myeloid cells outside the bone marrow. It is often an extramedullary manifestation of acute myeloid leukemia, and imaging lacks specificity, leading to potential misdiagnosis. Case Presentation A female patient diagnosed with mixed-phenotype acute leukemia achieved complete remission after chemotherapy and allogeneic hematopoietic stem cell transplantation. However, a relapse occurred in the breast after transplantation. The patient achieved local control through mastectomy and removal of the axillary lymph nodes on the affected side. Unfortunately, during the subsequent course of chemotherapy, the patient died of a severe pulmonary infection caused by coronavirus disease 2019. Conclusion Continuous treatment and monitoring of mixed-phenotype acute leukemia patients are essential, especially for those with extramedullary manifestations (such as breast involvement).