Yesterday, the Food and Drug Administration (FDA) approved a new drug, Bosulif (bosutinib), to treat patients with Philadelphia chromosome-positive (Ph+) chronic myelogenous leukemia (CML). Bosulif is approved for patients in the chronic, accelerated or blast phase of the disease that has progressed with other therapies, including imatinib, which is a standard first-line treatment, or could not tolerate the side effects of other therapies.Patients with a genetic mutation, the Philadelphia chromosome, produce an enzyme called tyrosine kinase that promotes the growth and proliferation of abnormal white blood cells. These abnormal cells can then build up in the bone marrow and crowd out the normal, healthy cells that are necessary for fighting off infection.Bosulif is a tyrosine kinase inhibitor, which means it blocks the tyrosine kinase enzyme from signaling the production of these abnormal cells.The approval was based on a single phase 1/2 study of 546 adult CML patients who had progressed after prior therapy or could not tolerate the side effects of that therapy. All patients received Bosulif. After 24 weeks, 34 percent of patients who had previously been treated with imatinib experienced a major cytogenetic response (35 percent or less of cells in the bone marrow are Ph+). For those patients who had a major cytogenetic response at any time, 52.8 percent of them had maintained a response for at least 18 months. For patients in the accelerated phase who had been treated with imatinib, 33 percent had blood counts in the normal range after 48 weeks and 55 percent had normal blood counts with no evidence of leukemia. For those in the blast phase of CML, results were slightly less dramatic: 15 percent had their blood counts in the normal range and 27 percent had normal blood counts with no evidence of the disease.Common side effects include diarrhea, nausea and vomiting, low platelets and red blood cells, and fatigue.For more information, visit bosulif.com.