The Distribution of the Philadelphia Chromosome in Patients with Chronic Myelogenous Leukemia

Thirteen patients with chronic myelogenous leukemia continued to have the Ph¹ chromosomes in 90-100 per cent dividing marrow cells during drug-induced clinical remissions. The Ph¹ chromosome was present in erythroid as well as granulocytic marrow cells, and possibly in megakaryocytes.

The presence of Ph¹ chromosomes was also studied in cultures of peripheral blood. In six patients in relapse, 40 per cent of metaphases contained the Ph¹ chromosome, and the percentage of these cells corresponded roughly to the relative frequency of immature granulocytes in the blood. In contrast, during remission, few or no Ph¹ chromosomes were found in peripheral blood cultures, presumably because in the absence of immature granulocytes the dividing cells in the cultures originate from lymphocytes, as they do in normal blood.

It is suggested that the Ph¹ chromosome usually arises in a precursor cell common to the erythroid, granulocytic, and megakaryocytic, but not the lymphoid series of hemopoietic cells.