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• Chronic phase of chronic myelogenous leukemia - A complete hematologic response was observed in about 95% of patients and a major cytogenetic response was noted in about 60% of patients.
• Accelerated phase of chronic myelogenous leukemia - Approximately 70% of patients in the accelerated phase of chronic myelogenous leukemia who were treated with imatinib mesylate achieved a complete hematologic response but only 24% achieved a major cytogenetic response.
• Blastic phase of chronic myelogenous leukemia - Treatment of patients in blast crisis with imatinib mesylate resulted in a complete hematologic response in 30% and a major cytogenetic response in 16%.

Taken as a whole, the results of the clinical trials with imatinib mesylate are significantly better than those achieved previously with standard hydroxyurea or Interferon-alpha therapy. Consequently, the discovery and clinical development of imatinib mesylate marks a major milestone in the treatment of chronic myelogenous leukemia.

In addition to its efficacy for the treatment of chronic myelogenous leukemia, imatinib mesylate has a much better safety profile than Interferon-alpha. Only about 2% of patients treated with imatinib mesylate had to stop taking the drug because of severe side-effects. The most common side-effects (mostly mild or moderate) included:

• Nausea and vomiting
• Muscle cramps
• Skin rashes
• Aching bones and joints
• Myelosuppression (decrease in the number of white blood cells, red blood cells, or platelets in the blood or marrow)
• Edema (swelling of a part of the body)
• Fatigue

More recent information obtained by the U.S. Food and Drug Administration (FDA) suggests that Gleevec (imatinib mesylate) may cause severe congestive failure and left ventricular dysfunction in some patients. Patients with cardiac disease or risk factors for cardiac failure should be monitored closely and any patient with signs and symptoms of cardiac failure should be evaluated and treated.

Dasatinib (Sprycel)

In June 2006, the U.S. Food and Drug Administration (FDA) granted accelerated approval for dasatanib (Sprycel) - a new oral treatment for patients with chronic myelogenous leukemia (CML). Sprycel is intended for patients with CML who are either no longer responding to, or who cannot tolerate, therapy with imatinib mesylate (Gleevec). The approval of Sprycel was based on four separate studies involving a total of 400 patients who were no longer responding to or could not tolerate treatment with Gleevec. For patients with the earliest stage of CML (chronic phase), treatment with Sprycel resulted in a response rate of 45% (either complete elimination or significant reduction of the number of leukemic cells). Approximately 31% of patients with advanced phases of CML also responded to treatment with Sprycel. Although these results are encouraging, studies are ongoing to determine whether treatment with Sprycel offers any clinical benefits in terms of survival or improvement of symptoms associated with chronic myelogenous leukemia.