Mast Cell Tumor Prognostic Panels

KIT staining patterns for MCTs. Upper left: grade I; upper right, grade II; lower left, grade III; lower right, negative control. Courtesy of Dr. Matti Kuipel, MSU.

Cutaneous mast cell tumors (MCT) are one of the most common tumors in dogs. Currently, prognostic and therapeutic determinations for MCTs are primarily based on the histologic grade of the tumor, but a vast majority of the tumors are of an intermediate grade, and the prognostic relevance is highly questioned, especially when pathologists assign the "grade II/high" category. Kiupel M, Webster JD et al; The use of KIT and tryptase expression patterns as a prognostic tool for canine cutaneous mast cell tumors. Vet Pathol 41[4]:371-7, 2004 July.

Dr. Matti Kiupel and his colleagues at MSU currently recommend a battery of tests on any mast cell tumor removed or biopsied. These tests include the following: PCR for c-kit mutation (tumors caused by c-kit mutations are highly aggressive but respond well to tyrosine kinase inhibiting therapies), KIT immunohistochemistry (see pictures above), immunohistochemistry for Ki67, AgNOR count, and PCNA (determines cell-cycle phase of proliferating cells). While there is some association between each independent test, prognoses developed from the interpretation of all the above listed tests offer us the highest level of certainty.

At ACIC, we also recommend that prognostic panels be performed on all mast cell tumors. It is especially helpful when pet owners are on the fence about whether or not to pursue additional surgery or treatment. For example, we are less likely to take a "monitoring approach" with a patient that had a mast cell tumor removed that was reported to be a grade II with clean, but narrow margins, if the prognostic panel indicates the potential for more aggressive biologic behavior. This particular patient should go back to surgery to obtain wider margins. Although the panels add additional cost for the client, they are extremely valuable in making treatment decisions that are best for the patient.