FUS-ERG gene fusion in isolated myeloid sarcoma showing uncommon clinical features

FUS-ERG gene fusion has not been reported in cases of myeloid sarcoma (MS), a subtype of acute myeloid leukemia involving extramedullary anatomic sites. Here, we report a case of a 48-year-old man with primary isolated MS of the anterior mediastinum, who later developed multiple extramedullary recurrences without bone marrow infiltration throughout the course. G-banding analysis of the cells in pericardial effusion at recurrence showed complex karyotypic abnormalities including t(16;21)(p11.2;q22). FUS break-apart fluorescent in situ hybridization analysis showed split signals in biopsy sections at initial diagnosis and recurrence. Reverse transcriptase polymerase chain reaction and direct sequencing demonstrated the presence of the FUS-ERG chimeric gene transcript. The patient underwent cord blood transplantation, but died of pneumonia on day 64. To our knowledge, this is the first report of isolated MS carrying FUS-ERG gene fusion. In future study, relationship between the fusion gene and uncommon clinical features should be investigated in isolated MS.