Early Relapse with Isolated Myeloid Sarcoma in a Patient Diagnosed Acute Myeloid Leukemia with FLT3- D835Y Mutation

Introduction: FLT3-TKD (tyrosine kinase domain) mutations are identified in approximately 4% of acute myeloid leukemia (AML) cases, and their prognostic significance remains unclear. While the association between myeloid sarcoma (MS) and FLT3-ITD positivity has been well documented, there is currently no definitive data regarding the relationship between FLT3-TKD mutations and MS, nor their impact on prognosis. We aim to present a case of a pediatric AML patient with the FLT3 D835Y mutation who initially presented with symptoms of mastoiditis and was subsequently diagnosed with MS. Case Presentation: An 11-year-old male patient with AML harboring the FLT3 D835Y mutation was in remission following treatment according to the AML-BFM 2019 protocol. After completing five cycles of chemotherapy, he was on maintenance therapy and receiving sorafenib. In the third month of maintenance, he presented to the emergency department with complaints of left ear pain and hearing loss. Initial suspicion was otomastoiditis, and he was treated with antibiotics. However, due to the persistence of symptoms, a biopsy was performed, which confirmed the diagnosis of MS. There was no evidence of bone marrow involvement. The patient was treated with chemotherapy and radiotherapy and was subsequently referred for bone marrow transplantation. Unfortunately, he passed away one month after transplantation due to sepsis. Conclusion: When mastoiditis-like symptoms appear in a patient with a history of AML, clinicians should consider the possibility of MS, particularly in cases with rare mutations such as FLT3 D835Y. Although the prognosis is generally poor, hematopoietic stem cell transplantation may offer a chance for cure. This case is noteworthy due to the uncommon immunophenotypic features and the rare localization of MS in the mastoid region.