Further evidence for the existence of a clonal Ph-negative stage in some cases of Ph-positive chronic myelocytic leukemia.

The Ph chromosome abnormality is involved in the pathogenesis of almost all patients with chronic myelocytic leukemia (CML). Previous studies on the B-lymphoid cell lineage in two patients with Ph-positive CML suggest that there may also be a clonal Ph-negative stage in CML and that the Ph-positive stage arises by subclonal expansion. To determine whether this is a frequent or a rare occurrence, 14 additional glucose-6-phosphate dehydrogenase (G6PD)-heterozygous patients with CML were studied. In five of these patients there was a statistically significant excess of Ph-negative B-lymphoid cell lines expressing the same G6PD type expressed in the corresponding CML clone. In no case was an excess of B-lymphoid lines expressing the opposite G6PD type recovered. These data provide further evidence that in some patients the Ph chromosome arises in a pluripotent stem cell from a pre-existing Ph-negative clone that enjoys a growth advantage.