The FDA has approved Pfizer’s Bosulif (bosutinib) to treat chronic myelogenous leukemia (CML), a blood and bone marrow disease that usually affects older adults.

Bosulif is intended for patients with chronic, accelerated or blast phase Philadelphia chromosome-positive CML who are resistant to or who cannot tolerate other therapies, including imatinib. Bosulif works by blocking the signal of the tyrosine kinase that promotes the development of abnormal and unhealthy granulocytes.

“With the approval of tyrosine kinase inhibitors, we are seeing improvements in the treatment of CML based on a better understanding of the molecular basis of the disease,” said Richard Pazdur, M.D., director of the office of hematology and oncology products, Center for Drug Evaluation and Research, FDA. “These improvements have been observed in chronic and accelerated phases of CML.”

The safety and effectiveness of Bosulif was evaluated in a single clinical trial that enrolled 546 adult patients who had chronic, accelerated or blast phase CML. All patients had disease that progressed after treatment with imatinib or imatinib followed by dasatinib and/or nilotinib, or who could not tolerate the side effects of prior therapy. All patients in the trial were treated with Bosulif.

In patients with chronic phase CML, efficacy was determined by the number of patients who experienced a major cytogenetic response (MCyR) within the first 24 weeks of treatment. Results showed 34% of patients who had been previously treated with imatinib achieved MCyR after 24 weeks. Of the patients who achieved MCyR at any time, 52.8% had their response last at least 18 months. Among patients previously treated with imatinib followed by dasatinib and/or nilotinib, about 27% achieved MCyR within the first 24 weeks of treatment. Of those who achieved MCyR at any time, 51.4% had their MCyR last at least nine months.

In patients with accelerated CML previously treated with at least imatinib, 33% had their blood counts that returned to normal range (complete hematologic response) and 55% achieved normal blood counts with no evidence of leukemia (overall hematologic response) within the first 48 weeks of treatment. Meanwhile, 15% and 28% of patients with blast phase CML achieved complete hematologic response and overall hematologic response, respectively.

The most common side effects observed in those receiving Bosulif were diarrhea, nausea, a low level of platelets in the blood (thrombocytopenia), vomiting, abdominal pain, rash, low red blood cell count (anemia), fever and fatigue.