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CHMP Recommends Conditional Marketing Authorization for Pfizer's Leukemia Drug

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Originally published Jan. 18.

EU's Committee for Medicinal Products for Human Use this week recommended that the European Medicine's Agency grant conditional marketing authorization for Pfizer's leukemia drug bosutinib.

The drug, approved four months ago by the US Food and Drug Administration under the brand name Bosulif (PGx Reporter 9/5/2012), is indicated for patients with chronic phase, accelerated phase, and blast phase Philadelphia chromosome-positive chronic myelogenous leukemia who have received treatment with one or more tyrosine kinase inhibitors and who are non-responsive to Gleevec (imatinib), Tasigna (nilotinib), and Sprycel (dasatinib).

Ph-positive CML is caused by a genetic mutation — the Philadelphia chromosome — that produces the defective BCR-ABL kinase, which produces too many abnormal white blood cells. Bosulif inhibits the BCR-ABL kinase as well as Src-family kinases.

Bosutinib has received orphan drug status from regulatory authorities in the US and in the EU.

With EU regulatory authorities, Pfizer submitted data from Study 200, a single-arm, open-label Phase 1/2 study of bosutinib in more than 500 patients with Ph+ CML with separate cohorts for chronic, accelerated, and blast phase disease previously treated with one or more prior TKIs. All study participants received bosutinib.

In the study, Pfizer researchers gauged efficacy in terms of the number of patients who experienced a major cytogenetic response within the first 24 weeks of treatment. Among those who had previously been treated with Gleevec, 34 percent achieved MCyR after six months. Of those who achieved MCyR at any time, 52.8 percent maintained their response to bosutinib for least 18 months. Of the patients who were treated with Gleevec followed by Tasigna or Sprycel, approximately 27 percent experienced MCyR within the first six months, and among those who achieved MCyR at any time, 51.4 percent experienced MCyR for at least nine months.

Around 33 percent of patients with accelerated CML previously treated with at least Gleevec had their blood counts return to normal range (complete hematologic response) and 55 percent had normal blood counts with no evidence of leukemia (overall hematologic response) within the first 48 weeks of treatment. Additionally, among patients with blast phase CML, 15 percent and 28 percent of patients saw a complete hematologic response and overall hematologic response, respectively.

Common side effects of bosutinib include diarrhea, nausea, thrombocytopenia, vomiting, abdominal pain, rash, anemia, pyrexia, and increased alanine aminotranserase.

"A pharmacovigilance plan for Bosulif will be implemented as part of the marketing authorization," CHMP said in a statement announcing the positive decision.

CHMP recommends conditional marketing authorization for drugs that attend to an unmet medical need. As such, the committee recommends speedy approval of the drug even though late-stage clinical trial data may not be available. CHMP recommends marketing authorization with the understanding that the drug sponsor will provide complete clinical data when available.

"Pfizer is in discussions [with regulatory authorities] on a post authorization study to generate additional efficacy and safety information in patients with Ph-positive CML previously treated with one or more TKIs and for whom imatinib, nilotinib and dasatinib are not considered appropriate treatment options," a Pfizer spokesperson told PGx Reporter.

The European Commission will review CHMP's recommendation for bosutinib, and decide whether to finalize approval of the drug throughout the EU. Pfizer is expects the EC to issue a final decision in the next few months.

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