We report CD34-positive ''blastoma'' which developed in a patient with
idiopathic myelofibrosis (IMF), A 48-year-old woman was diagnosed as
having essential thrombocythemia, then the disease had transformed int
o IMF 41 months later, Finally, a subcutaneous tumor, composed of blas
tic cells positive for CD34 but negative for lineage-specific antigens
, developed without any evidence of systemic leukemia transformation.