Canine acanthomatous ameloblastomas (CAA), analogs of human ameloblastoma, are oral tumors of odontogenic origin for which the genetic drivers have remained undefined. By whole-exome sequencing, we have now discovered recurrent HRAS and BRAF activating mutations, respectively, in 63% and 8% of CAA. Notably, cell lines derived from CAA with HRAS mutation exhibit marked sensitivity to MAP kinase (MAPK) pathway inhibitors, which constrain cell proliferation and drive ameloblast differentiation. Our findings newly identify a large-animal spontaneous cancer model to study the progression and treatment of RAS-driven cancer. More broadly, our study highlights the translational potential of canine cancer genome sequencing to benefit both humans and their companion animals.