Absence of the human retinoblastoma gene product in the megakaryoblastic crisis of chronic myelogenous leukemia.

The human retinoblastoma gene (RB) product, which is involved in the control of cell cycle and tumor suppression, is constitutively expressed as a nuclear phosphoprotein in normal human cells. We examined leukemic cells from 22 patients with blast crisis of chronic myelogenous leukemia (CML) for alterations of the RB expression. Western blotting and flow cytometry with anti-RB-protein antibodies showed that all of five cases with megakaryoblastic crisis lacked the expression of the RB-encoded protein, whereas none of 17 cases with the other phenotypes such as myeloblastic or lymphoblastic crisis showed any abnormality. These findings suggest that megakaryoblastic transformation of CML might be lineage-specifically associated with loss of the RB protein.