The Dog Cancer Survival Guide (94 page)

Another possible reason for lymphoma relapse is infrequent and inadequate doses of chemotherapy. If drugs do not achieve high enough concentrations, they cannot be effective. This can happen, particularly in sites deep in the body, such as the central nervous system (the brain and spinal cord).

If a dog has relapsed, the owner usually wonders whether to start chemotherapy again (called a rescue protocol). It is helpful to know that, in general, the likelihood of a second remission (or re-induction) is 50% and the second remission usually lasts 50% as long as the first.

A small number of dogs, especially if off chemotherapy at the time of relapse, after experiencing a complete remission, enjoy a longer second remission. For example, I have treated dogs who experienced an eleven-month remission, relapsed, and then enjoyed a nineteen-month remission. One patient, Lola, was put on prednisone by an emergency clinic to treat her lymphoma, and then came to me for a twenty-five week UW-CHOP rescue protocol. It has now been over two years since her last chemotherapy, and she has even developed a low-grade soft tissue sarcoma, which was successfully surgically removed during that time. I have another client who just celebrated her dog’s eleventh birthday; I treated Jabba the Mutt six years ago with two UW CHOP protocols. Cases like Lola’s and Jabba the Mutt’s, while not the statistical norm, give us real reason to be cautiously optimistic about lymphoma rescue protocols.

Another relevant decision is whether to repeat the same protocol, or to try new drugs. This depends upon how long the dog’s remission lasted. For example, if your dog completed a protocol like the UW CHOP protocol and experienced a long remission, I typically recommend using the same protocol again, because it worked the first time. This way you can save new drugs for a possible future relapse. However, if the dog does not achieve what is called a “durable remission” – a remission that lasts fourteen to twenty-one days – I recommend switching drugs. If your dog responds for only a few days or a week, this is not considered a good response, and I would look for another rescue protocol. Similarly, if your dog comes out of remission one month after completing the CHOP protocol, I typically recommend moving on to a new protocol. Common rescue protocols include: MOPP, MVPP, oral lomustine, doxorubicin, mitoxantrone and actinomycin-D.

“Do everything you can, read the book, cook the food and pray. We enjoyed nearly three times as much time with Tyler as originally diagnosed. Fight with your own vet over treatment, they are not aware of this research and will tell you there is nothing that can be done. THEY ARE WRONG.”

- John Arquette, Fayetteville, New York

From my perspective as a veterinary oncologist, lymphoma is highly treatable. Owners in my practice are typically extremely pleased with their decision to treat this cancer.

I rarely answer the question “would you treat this cancer, if this were your dog,” because I cannot compare my resources to those of clients: I’m an oncologist, my husband is a veterinary internist, one of my closest friends is a veterinary surgeon, and I have the support of many specialists at my disposal. Yet, I make an exception in the case of lymphoma and readily answer “yes, I would treat this cancer, if this were my dog.”

When aggressive chemotherapy treatment is balanced to maximize tumor kill and minimize serious side effects, dogs generally tolerate treatment well and live much, much longer than they would if they did not receive treatment.

During the weeks of chemotherapy treatments, most dogs’ experiences parallel their normal lives. Interestingly, owners often report that dogs have more energy during treatment than during the previous months, even year, when lymphoma was not clinically present.

Dogs may get sick from treatment, but, in order for them to live longer (and well), they require chemotherapy. I truly believe the benefit of treating dogs with lymphoma easily outweighs the risk of side effects. Even if the dog gets sick, he typically recovers and can continue therapy. Treated dogs live significantly longer, are happy, run, play, sleep and eat, much as they did before they got sick.

M
ast cell tumors (MCT) are cancers of mast cells, special immune system cells, heavily involved with inflammation and allergic reactions. Tumors most commonly develop in the skin, especially on the trunk, and can occur anywhere in the body. Mast cell tumors are also known as mastocytoma, mast cell sarcoma and systemic mastocytosis (or metastatic MCT).

While long-term survival is more common with MCT than with other dog cancers, MCT is a tricky cancer to predict. For example, some dogs with low or intermediate grade MCT have tumors that can be cured with surgery. They never recur or metastasize, or, if they do, it can be two to five years after the initial treatment.

Other dogs – about 10-15% – develop multiple skin tumors all at once, or over the months or years, never experiencing internal metastasis. Others develop multiple skin tumors over time, then internal metastasis eventually occurs. Still other dogs experience a higher grade of MCT with aggressive, malignant tumors that cause a rapid deterioration in health within months, and occasionally, within weeks. Because of this wide variance in outcomes, proper staging of MCT is important to determine your dog’s prognosis.

Traditionally, MCT is first treated with surgery to remove the primary tumor. The use of radiation therapy after surgery is very effective to prevent recurrence, especially if the tumor is on a limb; chemotherapy can also be helpful for some dogs. Especially for lower grades, I consider MCT a highly treatable cancer. Exciting new treatment options have recently come on the market, including Palladia, a new tyrosine kinase inhibitor, designed especially for dogs with MCT.

Mast cells play an important role in inflammation. While other immune system cells tend to circulate throughout the body, mast cells don’t – once they mature, they take up residence in specific tissues. Many live in tissues that mark the boundary between the outside environment and the internal environment, for example: the skin, the mouth, the digestive tract, the nasal passages and the lungs.

Mast cells contain structures inside their cell walls, called granules, which are like little sacks. These granules are filled with substances, or cytokines, including heparin and histamine, which help the immune system respond to problems. Heparin is a blood thinner which helps defend the body against foreign invaders, and histamine is a chemical that triggers inflammation. Normal mast cells release these substances when prompted by the immune system. In addition to their role in inflammation, mast cells are involved in allergies, anaphylaxis (systemic inflammation), the healing of wounds and defense against outside pathogens.

When you need to look up the definition of a word or phrase, find it listed in
Chapter 5
, which begins on
page 46
.

Mast cell tumors are cancerous accumulations of mast cells with a malignant potential. While MCT is very rarely found in humans, it is the most common malignant skin tumor in dogs, accounting for 15-20% of all skin tumors. Mast cell tumors first occur in the skin and the subcutaneous tissues beneath the skin. It’s very rare to find MCT in internal organs without a primary skin tumor, and skin tumors do spread to the regional lymph nodes, the spleen, the liver, other places deep in the abdomen and to the bone marrow.