Chronic myelomonocytic leukemia with a chromosome abnormality (46,XY,20q-) in all dividing myeloid cells: evidence for clonal origin in a multipotent stem cell common to granulocyte, monocyte, erythrocyte, and thrombocyte.

In a typical case of chronic myelomonocytic leukemia (CMML), a chromosome abnormality, 46,XY,20q-, was observed in all the dividing cells including up to 16-ploid cells in the bone marrow and the blood. As the mitotic figures could be easily seen not only in myelomonocytoid cells but also in erythroblasts in the bone marrow smear, it was concluded that all the cell lineages except lymphocytes had the abnormality. The present case will support the view that the leukemic process in CMML affects a multipotent stem cell rather than a granulocyte-monocyte committed stem cell.