Distinguishing the Philadelphia Chromosome of Acute Lymphoblastic Leukemia from Its Counterpart in Chronic Myelogenous Leukemia

Abstract

To the Editor: The Philadelphia chromosome (Ph), present in over 90 per cent of patients¹ with chronic myeloid leukemia, results when a small part of the long arm of chromosome 22 is replaced by a larger fragment derived from chromosome 9, containing the c-abl oncogene.² In all Ph-positive patients with chronic myelogenous leukemia thus far examined, the breakpoint of chromosome 22 is located within a 5.8-kb region, referred to as the bcr.³ Even in a Ph-negative patient, Southern blot analysis showed rearrangement of the bcr locus, resulting from a joint translocation of bcr and c-abl to chromosome 12. . . .