Successful long-term management with toceranib phosphate of a recurrent muzzle mast cell tumour in a dog

A 10-year-old spayed female Yorkshire terrier with a muzzle mass was presented. The ulcerated mass was surgically resected, but recurred and grew rapidly over the subsequent 7 months. The submandibular lymph nodes were remarkably enlarged (right: 9.5 × 7.8 cm; left, 4.7 × 4.0 cm). The cytological analysis of the mass and lymph nodes revealed a high-risk mast cell tumour characterised by high mitotic figures (> 5/oil immersion field), nuclear pleomorphism, multi-nucleation, karyomegaly, and anisokaryosis. A polymerase chain reaction analysis targeting the c-kit domain revealed an exon 8 mutation. The resection of the mass was not considered optional because of the location. Oral toceranib (3.25 mg/kg, every other day) and prednisolone (1.0 mg/kg to 0.5 mg/kg, once a day) were administered, and the mass disappeared within 1 month. Subsequently, the toceranib therapy was stopped for 4 months due to neutropenia (0.7 × 109/l). However, the mass recurred and the toceranib was resumed at the original dose, without affecting the neutropenia. No recurrence has been observed at the 16 months' follow up. Despite the persistent neutropenia, no clinical symptoms have presented. This is another report of the successful treatment of a recurrent muzzle MCT with toceranib in a dog.