Clinical, histological, immunohistochemical and genetic factors associated with measurable response of high-risk canine mast cell tumours to tyrosine kinase inhibitors.

The aim of the present prospective-retrospective study was to evaluate the response of high-risk canine mast cell tumours (MCTs) to tyrosine kinase inhibitors (TKIs) and to correlate this with prognostic factors. A total of 24 dogs presented with macroscopic cutaneous MCTs at disease stage II or III, and therefore, at high-risk of associated mortality, were included in the study and treated with masitinib (n=20) or toceranib (n=4). A total of 12/24 dogs achieved an objective response and the overall survival (OS) for all subjects was 113 days. Dogs responding to treatment had a significant increase in OS compared to non-responders (146.5 days vs. 47 days, P=0.02). Internal tandem duplications in exon 11 of the c-kit gene were identified in 6/24 cases. Ki67, KIT immunolabelling and c-kit mutation did not provide information regarding prognosis or prediction of response to TKIs in this population. Initial response to TKIs appears to be the most reliable prognostic factor for survival duration.