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.

Don't be afraid to explore (for Cash's mom!)

Hello everyone! I have just completed 4 evening lectures over the past several weeks so it's been hectic for me and the reason for no recent posts!

I wanted to share with you a recent case that presented to our hospital for a second opinion. It brings an excellent point home about the value of exploratory surgery. The patient had an ultrasound prior to referral to our hospital and thought to have a large liver tumor. The client was informed at the previous hospital that the tumor was probably inoperable and the risk of exploratory was extremely high because the patient would likely have massive bleeding.

On presentation to Dr. Walshaw for a second opinion, the patient was in relatively good health other than the suspected mass. Our ultrasound revealed that the mass appeared to be associated with the spleen. It can sometimes be difficult to determine the origin of a mass when it becomes very large - it can appear to be involving one organ when in fact it's only closely adjacent to it. In addition, as discussed in my previous post, even massive liver tumors can be removed. So, for this reason it is better to pursue exploratory surgery than just assume a tumor can't be removed or assume that nothing more should be done beyond the ultrasound. In this patient's case, not only was the tumor associated with the spleen and easily removed, the histopathology (biopsy) report revealed that it was benign - therefore surgery cured the dog. Without surgery, the patient's benign tumor could have ruptured and caused a deadly bleed.