In an extension of a short-term study examining the response of mast cell tumors (MCTs) in dogs to masitinib (a tyrosine kinase inhibitor), investigators from the University of Tennessee's College of Veterinary Medicine recently published their findings evaluating tumor response and overall survival rate and time for dogs with nonresectable MCTs treated with masitinib.
Participating client-owned dogs had nonresectable grade 2 or 3 MCTs. Placed in randomly selected groups, the dogs received daily oral masitinib or placebo until tumor progression was detected. Treatment was extended beyond an initial short term, six-month study, at which point tumor assessment was conducted at three-month intervals for each dog until detection of tumor progression.
Masitinib administration significantly improved survival rate in these dogs, with 62.1% of the treated dogs alive at 12 months and 39.8% alive at 24 months. In comparison, only 36% of the untreated dogs were alive at 12 months and 15% at 24 months. In contrast to the poor predictive value of tumor response at six weeks, tumor control at the six-month evaluations appeared to be highly predictive for 24-month survival. Additionally, indicating a possible cure, 9% of the treated dogs achieved complete responses at 24 months. Improved long-term survival was seen regardless of c-Kit status, although, in dogs with mutated c-Kit, the improvement was more obvious.
The authors of this study emphasize that the results of this clinical study suggest that short-term response should not be the determining factor for drug approval and that tumor response is not a substitute for ascertaining data on survival. They further caution that with regard to cancer drugs used to treat MCTs in dogs, efficacy should not be concluded based on short-term tumor response, which may be entirely irrelevant.
Hahn KA, Legendre AM, Shaw NG, et al. Evaluation of 12- and 24-month survival rates after treatment with masitinib in dogs with nonresectable mast cell tumors. Am J Vet Res 2010;71(11):1354-1361.
Link to abstract: http://avmajournals.avma.org/doi/abs/10.2460/ajvr.71.11.1354