Chronic Myelogenous Leukemia: Disease Biology and Current and Future Therapeutic Strategies.

Over the last 2 decades, four major therapeutic approaches have drastically changed the prognosis in chronic myelogenous leukemia (CML): 1) allogeneic stem cell transplant (SCT); 2) interferon alpha (IFN-alpha) based regimens; 3) donor lymphocyte infusions (DLI); and 4) and the revolutionary BCR-ABL tyrosine kinase inhibitors such as STI571 (signal transduction inhibitor 571). Each modality has exploited and targeted different aspects of CML biology, and is associated with different risk-benefit ratios. In Section I of this review, Dr. Melo reviews the molecular pathophysiology of CML and potential new targets for therapy including anti-sense strategies to disrupt the BCR-ABL gene and inhibition of the BCR-ABL tyrosine kinase activity. In Section II, Dr. Tura, addresses important questions in the use of IFN-alpha for the treatment of CML, including the mechanism of action and the development of resistance, the optimal dose and duration of therapy and the prediction of response based on clinical features. An approach to the choice of therapy based on the predicted mortality is presented. In Section III Dr. Giralt presents an update on the results of unrelated donor transplantion, donor lymphocyte infusions (DLI) and non-ablative stem cell transplantation (NST) in CML. The roles of CD8-depletion, dose escalation and the transduction of suicide genes in treatment with DLI are addressed. Early results of NST in CML show that it is feasible and can result in long-term disease control. In Section IV Drs. Kantarjian and Talpaz review the results of IFN-alpha plus low-dose cytosine arabinoside and other promising modalities for CML including homoharringtonine, decitabine, and polyethylene glycol-interferon. In Section V they present an update on the recent experience with STI571. Objective but transient responses have been seen in 40% to 50% of patients in CML blastic phase. In accelerated phase, the response rate with STI571 exceeds 70%, and these responses are durable. In chronic phase CML, STI571 at 300 mg daily in patients who failed IFN-alpha produces a complete hematologic response (CHR) in over 90% of patients. Early results suggest cytogenetic response rates of approximately 50%, which may be major in approximately 30%. The maturing results with STI571 may soon change current recommendations regarding the relative roles of established modalities such as allogeneic SCT and IFN-alpha. Important questions include 1) whether STI571 therapy alone may be sufficient to induce long-term survival and event-free survival in CML, or whether it needs to be combined simultaneously or sequentially with IFN-alpha and cytosine arabinoside; and 2) what should the indications for frontline allogeneic SCT be in relation to STI571 therapy.