What has been the only predictive marker that has been published to date in canine MCT?

• A. c-KIT mutational status
• B. p53 status
• C. Ki-67 index
• D. EGFR expression

Answer: (B)

In canine mast cell tumors, function of the p53 tumor suppressor pathway is a key determinant of tumor behavior. Abnormal p53 expression detected by immunohistochemistry tends to correlate with higher histologic grade, increased malignant potential, and shorter survival, making it the only biomarker with demonstrated predictive value in the published literature. Other markers have shown some associations in certain studies—such as c-KIT mutational status, Ki-67 proliferation index, or EGFR expression—but their prognostic findings have not been consistently validated across large or independent cohorts, so they haven’t established reliable predictive value. Thus, p53 status stands out as the best-supported predictor of outcome in canine MCT.