The US Food and Drug administration (FDA) have approved a tyrosine kinase inhibitor, toceranib phosphate (Palladia, Pfizer Animal Health), for use in dogs to treat cutaneous mast cell tumours. Unlike other cancer treatments for pets, this drug has not previously been used in humans and was developed specifically for the canine market. “This cancer drug approval for dogs is an important step forward for veterinary medicine,” said Bernadette Dunham, director of the FDA's centre for veterinary medicine ( Associated Press , 3 June 2009).

Toceranib phosphate inhibits KIT, vascular endothelial growth factor receptor 2 and platelet derived growth factor receptor-β, meaning that it has the potential to reduce tumour cell growth as well as tumour angiogenesis. “At the completion of a Palladia clinical study, approximately 60% of dogs had their tumours disappear, shrink or stop growing,” reported Dr Cheryl London of Ohio State University's College of Veterinary Medicine, USA, who worked on the study ( L.A. Times , 3 June 2009). However, despite either a complete or partial response in 62 of the 145 dogs that received Palladia, these tumours re-grew with a median time to progression of 18.1 weeks. Survival rates were not examined in this study.

These findings are “important for all pet owners,” said Lisa Peterson, a spokeswoman for the American Kennel Club. “It shows they are valued family members.” ( CBS News , 6 June 2009.) However, it remains to be seen how expensive this might prove to be for dog owners, as Pfizer is not expected to release the drug to the market until early in 2010.