Twenty-seven dogs with confirmed GISTs via histopathology and immunohistochemistry, treated with toceranib. Seven dogs had gross (measurable) disease while 20 dogs were treated in the face of microscopic (non-measurable) disease.

Methods:Retrospective study in which cases of toceranib use in canine GIST were solicited using the American College of Veterinary Internal Medicine Oncology and Small Animal Internal Medicine listservs. 

Results:Five of seven dogs with gross disease experienced clinical benefit (3CR, 1PR, 1SD). These included two dogs with durable responses following toceranib discontinuation. Median progression-free interval (PFI) in dogs with gross disease was 110 weeks (range 36-155). Median PFI in dogs with microscopic disease was 67 weeks (range 9-257). A single case with microscopic disease developed disease recurrence one year after stopping a planned course of toceranib therapy and was successfully treated with metastasectomy followed by reintroduction of toceranib. Metastasis at diagnosis (p = 0.04) and increasing mitotic index (p < 0.001) were associated with shorter PFI in toceranib-treated dogs.

Conclusions and clinical importance:Biological activity of toceranib is evident in dogs with gross disease. Metastasis of GIST at diagnosis, as well as increasing tumor mitotic index, were associated with a shorter PFI in toceranib-treated dogs.Larger studies are needed to define post-surgical risk and refine the use of toceranib in dogs with gross and microscopic GIST.