Granulocytic sarcoma of megakaryoblastic differentiation complicating chronic idiopathic myelofibrosis.

We report the development of soft tissue granulocytic sarcoma with megakaryoblastic differentiation in a patient with chronic idiopathic myelofibrosis, which has hitherto been undescribed. Although an artifactual signet ring appearance of the blasts was found in the formalin-fixed tissue and caused diagnostic problems, the histological appearance on B-5 fixed material and immunophenotyping confirmed the diagnosis. Cytogenetic analysis showed 47,XY,+der(1)del(1)(?p13) at initial presentation and 47,XY,del(1)(?13),+der(1)del(1)(?p13) at the time of soft tissue blastic transformation, indicating that partial trisomy 1 might be of pathogenetic significance.