The tyrosine kinase inhibitor imatinib [STI571] induces regression of xenografted canine mast cell tumors in SCID mice.

Canine mast cell tumors (MCTs) are the most common cutaneous tumors in the dog. They have a wide range of behaviour, which can make these tumors challenging to treat. Recently, mutations in c-kit proto-oncogene have been identified in several canine MCTs. Imatinib is the first member of a new class of agents that act by inhibiting particular tyrosin kinase enzymes, including KIT which is a product of the c-kit. In this study the efficacy of imatinib to reduce or abolish canine MCT [CMC-1] using xenografted MCT in severe combined immunodeficient [SCID] mice was evaluated. Imatinib was administered at doses of 200mg/kg and 100mg/kg once a day for one week. The antitumor responses in SCID mice with CMC-1 xenografts following treatment with imatinib were observed. Significant tumor regression occurred with 100mg/kg on days 7, 10, 14 and 21, and 200mg/kg on all days. Our results indicate that imatinib is effective against canine mast cell tumor in mouse xenograft models. Canine MCTs might be a potential target for imatinib therapy.