Enzyme negative blastic transformation of chronic myeloproliferative disorders: immunophenotyping of the blastic cell population.

Enzyme negative blast cells from 27 patients with chronic myeloproliferative disorders (CMPDs) in blastic transformation were analysed with a panel of monoclonal antibodies (MoAbs). According to morphologic features of the bone marrow and laboratory data, the 27 cases were divided into 8 cases of myelofibrosis (MF), 3 cases of chronic megakaryocytic granulocytic myelosis (CMGM) and 16 cases of chronic myeloid leukaemia (CML). Of the 27 cases, 23 showed a positive reaction with myeloid MoAbs, but in 12 cases expressing myeloid markers, megakaryocytic, monocytic or lymphoid cell features were also detected. In 7 cases of MF, 1 case of CMGM and 1 case of CML a bilineage, myelo-megakaryocytoid immunophenotype of peripheral blast cells was seen. Of the 4 patients with CML expressing lymphoid markers, 2 showed early B-cell, 1 T-cell surface antigens, and 1 both myeloid and early B-cell features. In this group of cytochemically immature blastic transformation of CMPD, only 1 case was termed "undifferentiated" blastic transformation.