Extramedullary Megakaryoblastic Tumors Following an Indolent Phase of Myelofibrosis

A 59-year-old man developed multiple subcutaneous and bone tumors after 2 years' duration of indolent myelofibrosis. These tumors exhibited a diffuse proliferation of pleomorphic blast cells. The skeletal x-rays showed disseminated osteolysis and osteosclerosis. Blast cells obtained from the pleural effusion did not react with myeloperoxidase, sudan black B or non-specific esterase. Genotypic analysis of DNA samples at autopsy did not demonstrate rearrangements of T-cell receptor beta-chain or immunoglobulin heavy-chain genes. Frozen-section immunohistochemical studies revealed that the neoplastic cells were derived from megakaryocytic lineage. The present case represents a novel and unusual subtype of megakaryocytic neoplasm.