The Dog Cancer Survival Guide (97 page)

The conventional treatments Dr. Ettinger recommends for mast cell tumors are to be considered part of step one of Full Spectrum cancer care (
Chapter 11
). Please review that chapter for more general information about surgery, radiation and chemotherapy and how to handle their common side effects.

For more information on all other Full Spectrum steps, including nutraceuticals, immune boosters, dietary changes and brain chemistry modification strategies, review Full Spectrum cancer care, which begins on
page 103
.

You will also find information about specific chemotherapy agents in
Chapter 41
.

For more advanced MCT cases, I may recommend chemotherapy in addition to surgery and radiation, and occasionally instead of those therapies. This is common for grade III MCT, for example. However, I sometimes also use it for grade II MCT with high proliferation marker scores or for multiple skin MCTs, which is a less common, and even controversial, practice. I decide this on a case-by-case basis, and have had success with vinblastine, prednisone, Lomustine, and the new tyrosine kinase inhibitors, Palladia and masitinib (Kinavet CA-1).

Two of these are worth special mention, because they can be very beneficial for MCT. Masitinib, trade name Kinavet CA-1, is a new drug in the United States (conditionally approved by the FDA in December of 2010) but already approved in Europe for MCT. Prior to approval, U.S. oncologists were able to get it through the FDA’s compassionate use program, so most are familiar with the drug.

Palladia is available in the U.S. and is FDA-approved specifically for dogs with recurrent, Grade II and Grade III MCT, with or without regional lymph node involvement. Palladia works in two ways to fight MCT: it cuts off blood supply to MCT by blocking angiogenesis, and it also inhibits tyrosine kinase, a protein which stimulates tumor growth. One-third of dogs with MCT have a genetic mutation (c-Kit) that leads to tyrosine kinase being stuck in the “on” position, leading to increased survival for mast cell tumors. Palladia’s is particularly helpful for these dogs. In fact, Palladia (along with masitinib) is part of a new class of drugs named for this ability: tyrosine kinase inhibitors (TKI).

Overall, 60% of the dogs treated with Palladia alone in clinical studies had their MCT disappear, regress or stabilize (stop growing), and this result was seen even in dogs who did not have the c-Kit mutation. In addition to the effect on the tumors, quality of life improved for these dogs, who experienced more energy and better attitude.

Palladia is a relatively new drug and I’m excited about its results, so far. Because drugs often work even better in combination, Palladia’s use in combination with other chemotherapy drugs is now starting to be evaluated to see if it helps microscopic cancers and metastatic cancers. Of course, the risk of possible side effects increases when you combine drugs, so if you contemplate this, I recommend doing so with an oncologist’s supervision.

In addition to surgery and radiation, and possibly chemotherapy, you may want to consider supportive medications to counteract the effects of possible degranulation (when the mast cell tumor breaks open). The following are especially helpful for dogs with large tumors, detectable spread, and systemic signs such as vomiting: anti-histamines (such as Benadryl), antacids (such as Pepcid) and proton pump inhibitors (such as Prilosec). These can often be stopped after surgery, if the tumor has been successfully removed and spread has not occurred; some dogs may need these drugs long-term to control their symptoms.

Ten to fifteen percent of canine MCT cases (all grades) develop additional masses after their first mass is removed, and metastasis is also possible. Because of this, I recommend all dogs with MCT receive rigorous check-ups every three to six months for the rest of their lives to check for new masses, recurrence and spread. If a new mass is discovered in between checkups, definitely get it aspirated and evaluated.

From my perspective as a veterinarian oncologist, mast cell tumors are highly treatable. Aggressive surgery is required, with wide margins, and may be the only treatment needed. Radiation treatments and/or chemotherapy might be needed; dogs generally tolerate treatment well and live longer. The addition of tyrosine kinase inhibitors like Palladia to our treatment arsenal makes me even more optimistic about MCT. While there may be recurrence and/ or metastasis, long-term control and survival is definitely possible.

I believe the benefit of treating dogs with MCT easily outweighs the risk of side effects. Treated dogs live significantly longer, are happy, run, play, sleep and eat much as they did before they got sick.

“I am so sorry that you have to experience this; but don’t give up hope. You are your pet’s #1 advocate and as such it is your duty to research the current medications available and what research that is being conducted to combat this disease. My oncologist was not receptive to Dr. Dressler’s book but had never read it. Every bit of info I brought out in our initial conversation that I took from the book was info she could not dispute and often agreed with. I believe that the more knowledgeable the owner is about their pet’s situation, the more willing the doctor will be to pursue other avenues. This is merely my opinion, but it makes sense that doctors are more willing to try different medications with owners who are more interested in their pets’ health than with other owners who merely “go with the flow.” Also, many owners are capable of asking very intelligent questions that their doctor may not have considered.”

-Debbie Granger, Chesterfield, Missouri

M
ammary tumors can develop in several types of cells found in the mammary glands of female dogs. These tumors are also called mammary gland tumors or simply, breast cancer.

Many mammary tumors are responsive to treatment because about half are benign, and about half of those that are malignant, do not metastasize. Surgery is the primary treatment for mammary tumors.

Survival times vary widely, depending upon several prognostic factors. Generally, dogs with benign tumors have significantly longer survival times than those with malignant tumors.

Mammary tumors are among the most common tumors found in female dogs – in fact, dogs are three times more likely to develop mammary tumors than are human women. As you probably know, mammary glands produce breast milk for nursing young. While male dogs do have these glands, they rarely develop mammary tumors; only one percent of all cases occur in males.

Most dogs have ten mammary glands, five on each side (or “chain”). Mammary glands are complicated structures, made up of several types of cells, all working together. Tumors can develop in any of these cells, so, mammary tumors come in many different forms.

About fifty percent of all mammary tumors are benign. The most common are: adenomas, which arise in the epithelial tissue lining the glands; cystoadenomas (also called cystadenomas), which arise in the epithelial tissue in the milk-producing structures, and often form fluid-retaining cysts; and mixed mammary tumors, which develop when tumors arise in both epithelial and connective tissues.