Acquired RUNX1::CBFA2T2 fusion at extramedullary relapse in a patient of PDGFRA rearranged acute myeloid leukemia post allogenic HSCT

FIP1L1::PDGFRA rearranged myeloid neoplasms encompass a broad range of malignancies including chronic eosinophilic leukemia, MDS, MPN, MDS/MPN, AML and myeloid sarcoma. A little data are available pertaining to their antigen expression pattern till now due to low disease incidence. We hereby, describe a post-transplant case of FIP1L1::PDGFRA rearranged AML that had a typical extramedullary relapse with an additional RUNX1::CBFA2T2 fusion within the first year of post-transplant period and presented with a peculiar CD45 negative immunophenotype. A 25-year-old male patient of FIP1L1::PDGFRA rearranged AML, on follow-up day 280 of post allogenic hematopoietic stem cell transplant (allo-HSCT) presented with palpable left cervical lymphadenopathy and multiple subcutaneous nodules over chest, abdomen and bilateral lower limbs averaging from 0.5 to 1 cm in maximum dimen-sion. High-resolution computed tomography of thorax revealed bilateral pleural effusion and a solitary right lung upper lobe nodule measuring 1.0 (cid:1) 0.9 cm and multiple discrete mediastinal lymph nodes. Complete blood counts showed hemoglobin 11.5 g/dL, total leukocyte count 5.61 (cid:1) 10 3 / μ L, platelet count 110 (cid:1) 10 3 / μ L and no blast on peripheral blood (PB) differential leukocyte count. Bone marrow (BM) morphology was unremarkable and multicolor flow cytometry (MFC) measurable residual disease was negative. Neither PB nor BM showed any increase in eosinophil count. Liver function test showed