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Veterinary Forum June 2009 (Vol 26, No 6)

EMEA approves mast cell drug; compassionate use available in US

by Marie Rosenthal, Belinda Burwell, DVM

    The European Medicines Agency (EMEA), Veterinary Medicines and Inspections unit, recently granted marketing approval to AB Science for its new oncology drug, masitinib.

    Masitinib, which will be marketed in Europe under the name Masivet, is indicated for the treatment of grade II and grade III mast cell tumors in dogs. This is the first targeted oncologic therapy to be approved for veterinary use, although such therapies have been prescribed in human medicine for several years.

    The EMEA approval was based on quality, safety and efficacy data showing that masitinib extended survival in dogs with nonresectable mast cell tumors. A number of studies were conducted in laboratory dogs or in patients at veterinary practices in Europe and the United States, according to the EMEA Public Assessment Report.

    The main study compared the efficacy of masitinib with a placebo in various canine breeds that had nonresectable mast cell tumors or tumors that had returned after surgery and/or chemotherapy. Dogs receiving masitinib at a dose of 12.5 mg/kg/day achieved better outcomes. Time to progression of a tumor that contained mutated c-kit receptors was extended in dogs that received masitinib (median 241 days) compared with dogs that received the placebo (median 83 days), according to the EMEA report.

    Mast cell tumor growth depends on a complex interaction between the neoplastic cells and surrounding tissue. According to Joseph A. Impellizeri, DVM, DACVIM (Oncology), medical director of the Veterinary Specialty Center of the Hudson Valley and a member of the Forum Editorial Board, many of the processes involved in tumor growth, progression and metastasis are mediated by ligand-receptor interactions involving enzymes, called receptor tyrosine kinases (RTKs), and downstream signaling molecules.

    Masitinib works by selectively inhibiting membrane receptors, including c-kit and platelet-derived growth factor receptors (PDGFR), and intracellular receptors, including Lyn tyrosine kinase enzymes. Some mast cell tumors are linked to a mutation that causes excessive action of c-kit, stimulating the mast cell to divide, accumulate, and release mediators uncontrollably. By blocking c-kit, masitinib can help control cell division and tumor growth.

    Masitinib also is under review for marketing approval by the US Food and Drug Administration for the same indication. Following approval, the drug will be marketed here to US veterinary specialists. Until then, masitinib is available to US veterinarians for compassionate use in cases that do not respond to current mast cell tumor therapy. For information about compassionate use under the FDA regulatory guidelines of personal import, contact Albert Ahn, DVM, president of AB Science USA at 973-218-2437 or by e-mail at albert.ahn@ab-science.com.

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