Acute undifferentiated leukemias (AUL) is the diagnosis of exclusion and is very rare, the morphology of leukemic cells is not specific. Here we report a rare case of AUL with myelofibrosis with an unusual morphology. A 40 year female presented with anaemia and hepatosple enomegaly with pancytopenia and leucoerythroblastic blood picture on peripheral blood smear underwent bone marrow studies. Bone marrow biopsy showed infiltration of blasts with scant cytoplasm, round to irregular nucleus, dispersed chromatin with grade 3 fibrosis by Reticulin stain and negative Masson trichrome stain. Immunohistochemistry (IHC) on bone marrow biopsy showed CD 34 positivity and negative for Tdt, MPO, CD3, CD20, CD61 markers. Thus diagnosed as Acute undifferentiated leukemia with myelofibrosis. AUL is the diagnosis of exclusion and before categorizing leukemia as undifferentiated, it is necessary to perform immunophenotyping with a comprehensive panel of monoclonal antibodies.
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