A case of nonleukemic myeloid sarcoma with FIP1L1-PDGFRA rearrangement: an unusual presentation of a rare disease.

Rearrangement of the PDGFRA gene defines a distinct group of hematopoietic neoplasms that commonly present with persistent eosinophilia and are highly sensitive to low-dose imatinib mesylate treatment. Although rare cases of PDGFRA rearrangement-associated acute myeloid or lymphoblastic leukemia can occur, nonleukemic myeloid sarcoma has not been reported, and its sensitivity to imatinib treatment is unknown. Herein, we report a 31-year-old man with nonleukemic myeloid sarcoma and marked peripheral blood and bone marrow eosinophilia. Fluorescent in situ hybridization studies demonstrated that both bone marrow hematopoietic precursors and blasts of the myeloid sarcoma were positive for FIP1L1-PDGFRA rearrangement. The patient consequently received imatinib treatment at a dosage of 100 mg daily. After 3 weeks of therapy, his eosinophilia and myeloid sarcoma completely resolved, and at evaluation after 3 months he had attained bone marrow cytogenetic remission. To our knowledge, this is the first case of a nonleukemic myeloid sarcoma with the FIP1L1-PDGFRA rearrangement. Despite its aggressive clinical behavior attributed to myeloid sarcoma in general, the presence of PDGFRA rearrangement in this case conferred a high sensitivity to imatinib treatment and a favorable clinical outcome.