Myeloproliferative Neoplasm with FIP1L1-PDGFRA Fusion Presenting as Extramedullary Acute Myeloid Leukemia (Myeloid Sarcoma) in a Lymph Node

Since its discovery 10 years ago, the FIP1L1-PDGFRA mutation has been associated with a wide spectrum of hematopoietic neoplasms which range from T-lymphoblastic leukemia/lymphoma, chronic eosinophilic leukemia, chronic myeloid leukemia, acute myeloid leukemia, myeloid sarcoma and systemic mastocytosis. Common between these neoplasms was eosinophila and sensitivity to imatinib and other tyrosine kinase inhibitors. Here, we discuss the case of 51 year old man who presented with nodal myeloid sarcoma mimicking lymphoma as the presenting feature of his FIP1L1-PDGFRA myeloid neoplasm. His pelvic lymph node contained a diffuse infiltrate of blasts while his blood contained a normal white count with only mild eosinophilia. Bone marrow showed a mixed picture with areas of diffuse blasts and other areas of myeloproliferative neoplasm with eosinophilic predominance. Fluorescent in-situ hybridization demonstrated the del (4q12) and fusion of FIP1L1 and PDGFRA. The patient was treated with single agent imatinib with complete response. Our case represents the first FIP1L1-PDGFRA myeloid sarcoma to present as lymphadenopathy and only the fifth case of FIP1L1-PDGFRA myeloid sarcoma in all. The persistent remission attained in our case using only single agent imatinib reiterates the importance of identifying this mutation.