c-KIT mutation in canine mast cell tumours: what it predicts
9-year-old Labrador with a recurrent mast cell tumour on the forearm, high grade (Kiupel), no longer resectable with margins. PCR on tumour tissue detects an internal tandem duplication in exon 11 of c-KIT.
Which statement about this finding is correct?
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A. Indicates a low-grade tumour with a good prognosis; monitoring is enough
The opposite: c-KIT exon 11 mutations are associated with higher histological grade, more recurrence and shorter survival.
B. Predicts better response to toceranib; wild-type tumours may also respond
Correct. Activating KIT mutations (mainly exon 11 duplications) make the tumour dependent on that signal, and mutated tumours respond more often to toceranib. Wild-type tumours respond less often, but its use is not ruled out.
C. Contraindicates tyrosine kinase inhibitors; vinblastine is preferable
The mutation is precisely the target of toceranib and masitinib. Vinblastine with prednisolone is a valid alternative, but the mutation does not make it preferable.
D. It is an inherited germline mutation and littermates should be tested
c-KIT mutations in mast cell tumours are somatic, acquired by the tumour cells. That is why they are tested in tumour tissue and not in blood.
lightbulb Key takeaway
Request c-KIT mutation analysis (exons 8 and 11) in high-grade, recurrent or non-resectable mast cell tumours: it adds prognostic information and helps choose a tyrosine kinase inhibitor. A negative result does not rule out trying toceranib.
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Updated: November 1, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.