Imatinib mesylate: clinical results in Philadelphia chromosome-positive leukemias

Targeted cancer therapy has long been sought by the oncology community as a potentially better approach than currently available therapies. One targeted therapy that has shown great success is the tyrosine kinase inhibitor imatinib mesylate (formerly STI571, [Gleevec]; Novartis Pharmaceuticals Corp, East Hanover, NJ) which was recently approved for the treatment of Philadelphia chromosome-positive chronic myeloid leukemia (CML). Basic scientific investigation into the molecular causes and pathogenesis of CML and encouraging preclinical investigations on the mechanism of action of imatinib mesylate led to the initiation of phase I clinical trials. Clinical development of imatinib mesylate continued with three large, multicenter, phase II trials. The majority (88%) of interferon-alpha-resistant or intolerant patients in chronic-phase CML achieved a complete hematologic response to imatinib mesylate. More importantly, approximately half of patients achieved a major cytogenetic response, a result historically associated with improved survival. Furthermore, 21% of patients in accelerated-phase CML and 13.5% of patients in blastic-phase CML (patient populations with typically poor prognosis before the advent of imatinib mesylate) achieved major cytogenetic responses. Results from ongoing studies will determine the durability of these responses and will evaluate ways to optimize treatment in advanced-stage patients using imatinib mesylate in combination with other therapies. Additional trials are planned to investigate the efficacy of imatinib mesylate to treat a variety of solid tumors whose pathogenesis is driven by the other tyrosine kinase targets, c-Kit and platelet-derived growth factor receptor.