Philadelphia chromosome-positive acute lymphoblastic leukemia.

The Philadelphia (Ph1) chromosome, ubiquitous in chronic myelogenous leukemia, also is commonly seen in acute lymphoblastic leukemia, particularly in adults. Whereas the presence of the Ph1 chromosome is associated with high white blood cell count and older age, the Ph1 chromosome is known to be an independent poor prognostic factor. Most Ph1+ patients are able to achieve remissions with intensive, systemic chemotherapy, but treatment is complicated by early relapse. Because of the uniformly poor prognosis and response to therapy in childhood and adult Ph1+ acute lymphoblastic leukemia, aggressive and investigational therapies should be considered early in the course of this disease.