BCR-ABL in chronic myelogenous leukemia--how does it work?

The discovery of the BCR-ABL fusion gene on the Philadelphia (Ph) chromosome in 1985 was the start of a new era in understanding the molecular basis of hematologic malignancies. It provided the rationale for producing first imatinib and then a series of small molecules designed to inhibit the tyrosine kinase activity of the Bcr-Abl oncoprotein, all of which can induce complete cytogenetic remissions in the majority of patients with chronic myelogenous leukemia (CML) in the chronic phase. However, we still do not know for sure whether the BCR-ABL fusion gene is really the initiating lesion for the chronic phase of CML and we have an incomplete understanding of the so-called genomic instability that underlies the production of the fusion gene and predisposes the Ph-positive clone to acquire further genetic events that lead to advanced-phase disease. Moreover, it is clear that though some of the mutant Ph-positive subclones that develop in patients taking tyrosine kinase inhibitors (TKIs) are the direct cause of the resistance observed, in other cases, its cause is unclear. It is likely that in the next few years we will see (1) improved methods for predicting responses to TKIs, (2) the use of TKIs in combination with other effective molecules such as farnesyl transferase inhibitors, and (3) a gradual reduction in the proportion of chronic-phase patients resistant to therapy. (c) 2008 S. Karger AG, Basel.