The Dog Cancer Survival Guide (42 page)

There are many potential chemotherapy side effects and it’s important to put them into perspective. I’ve never known a vet who wants to see dogs suffer needlessly, and there are ways to minimize or manage side effects (see the next section), so that therapy can continue, if you feel it is helping your dog. Remember, protocols can be changed – and are changed – depending upon how well your dog is doing, and side effects can be managed.

Cancer is so common in humans these days that most of us know someone who has gone through chemotherapy. If you do, it’s important to remember that humans tend to have more dramatic and intense side effects from chemotherapy than dogs do, because we don’t give dogs the curative doses we give to humans. Because of these lower doses, most dogs tolerate chemotherapy better than most humans do. Veterinary oncologists push for a fine balance between maximizing the cancer kill rate and minimizing the inevitable side effects. They are well aware that, if your dog feels sick all the time – or seems sicker from the treatment than she does from the disease – you will probably not want to continue treatments.

While most dogs do experience some side effects, they are generally mild. Most dogs will vomit or have some diarrhea, at least once or twice during the entire course of their protocol and this will often be managed by take home medications or natural products (see below).

In about 5% of cases, dogs get severe enough side effects to require hospitalization, where they are usually treated with intravenous fluids, antibiotics, and anti-nausea and anti-vomiting medications. Once they have recovered, chemotherapy doses may need to be lowered and more preventative medications may be needed.

Chemotherapy typically targets rapidly dividing cancer cells. Normal cells in the body also divide – making them vulnerable to chemotherapy’s effects, too. It’s the harm to these normal cells that causes side effects. Normal cells that rapidly divide carry the highest risk for side effects, and others can be affected, too.

If your dog has a history of problems with the liver, heart, kidney, blood cells, pancreas, lung, brain or any other medical condition, be sure to tell your oncologist about it. Chemotherapy drugs can have many effects in the body, and your vet or oncologist should be aware of all pre-existing problems in order to tailor your dog’s treatment correctly. Make sure your oncologist has access to your dog’s full medical history.

Here are the most common side effects:

• Intestinal Symptoms:
  The cells that line the digestive tract multiply very rapidly (completely replacing themselves every three days), which makes them very sensitive to chemotherapy. Nausea, vomiting, decreased appetite and diarrhea can result, and these are the most common and expected chemotherapy side effects. Symptoms usually start one to five days after a treatment and last for three days or more, while the intestines repair themselves. In most cases, the symptoms are mild and can be treated at home (see below). About 5% of dogs experience serious symptoms, such as not eating for more than twenty-four hours, vomiting three times or more in the span of a few hours or for more than twenty-four hours, a fever over 103° or severe, bloody, or black diarrhea or diarrhea for more than forty-eight hours. If your dog displays any of these symptoms, contact your vet immediately and get emergency help. In these rare cases, your dog may need to be hospitalized to receive IV fluids, antivomiting medications and other supportive care. There is more information on this important topic in the section on managing side effects, below, and oncologists usually send clients home with medications and detailed instructions on how to manage side effects and what warrants emergency care. For detailed instructions on how to take your dog’s temperature, please see
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• Bone Marrow Suppression:
  Bone marrow is the spongy material at the core of bones, which produces red blood cells, white blood cells and platelets. Most chemotherapy drugs cause some degree of suppression of its function, which can have system-wide effects. In most cases, bone marrow suppression happens, but is mild; it shows up in blood tests, although the dog does not have any symptoms. In more severe cases, the dog may not feel sick, but is at high risk for infections and sepsis. In rare cases, your dog may experience severe suppression, and you may have to call your vet. For example, several
  white blood cells
  (WBC) are important components of the immune system, so, when their levels drop, immune suppression occurs. Neutrophils are one type of WBC easily affected by chemotherapy. They protect against
  infection, so, if their levels drop – which is called neutropenia – fevers and infections can flare up. In severe cases, sepsis (a systemic infection) can set in. Symptoms of sepsis include: severe fever, depression, lethargy, vomiting, diarrhea and/or lack of appetite. This is a life-threatening emergency that requires hospitalization, which is why your vet should carefully monitor WBC levels by drawing blood for a complete blood count every time he administers chemotherapy and, sometimes, between treatments. For this reason, it is wise to take your dog’s temperature during chemotherapy (up to a week after the last treatment, especially if your dog has low white cells). Chemotherapy doses are based, in large part, on the neutrophil levels in the CBC – if levels are too low, the dose may be adjusted down. WBC usually will rebound on their own, a day or two after a session, and antibiotics can be given, along with chemotherapy, to offer protection from further drops. If antibiotics don’t help, a human medication called Neupogen may be recommended. Neupogen stimulates bone marrow to make neutrophils, and, like all medications, is considered on a case-by-case basis. Although Dr. Ettinger rarely prescribes it, she feels it is worth mentioning as a possible helpful tool for cases where extremely low white blood cell counts don’t improve on their own after a few days with supportive care. If
  red blood cell
  production goes down, anemia sets in. The cause of this is more often the cancer itself, rather than chemotherapy, but you should know about it. If it is severe, you may see low energy or lethargy, weakness, a decrease in appetite, panting and pale or white gums. (Red blood cells replenish themselves within five days, as long as the bone marrow can recover (which it usually can), and there is no cancer in the bone marrow.) If you notice symptoms like these, please call your vet or oncologist.
  Platelets
  help the blood to clot normally, so when platelet production drops, there is a higher risk for abnormal bleeding. Depending upon how low the platelet levels are, the symptoms can range from bruising easily, to blood in the stool, to internal hemorrhaging. If you notice symptoms like these, please call your vet or oncologist.
  
• Hair Loss:
  Otherwise known as alopecia, hair loss is a common side effect in humans who undergo chemotherapy. Luckily, it’s less common in dogs – and just as luckily, dogs don’t care about their hair like we do. If hair (or fur) loss occurs, the coat may thin out all over, or clumps of hair could fall out, exposing bald skin. Hair is usually slow to re-grow, especially in areas that have been shaved during treatments (for a catheter insertion, for example). When hair grows back, it may be of a slightly different color or texture. Many breeds do not typically experience alopecia during chemotherapy, while others are more prone to losing their hair, including Old English Sheepdogs, Poodles, Scottish Terriers, West Highland Terriers, and breeds whose hair needs a lot of clipping.
  

The traditional approach to chemotherapy is oriented toward the maximum tolerated dose (MTD). The idea is to administer the highest dose possible, in the shortest amount of time, without causing severe side effects or death.

Treatments given at MTD have to be spaced out, so that normal tissues, injured during the treatment, have a chance to heal. If those tissues take a long time to recover, the next treatment is delayed - and this can allow the tumors time to recover, as well.

Recently, we have adopted a new approach, called metronomic chemotherapy. This approach doesn’t attempt to kill cancer cells directly; instead, it tries to cut them off from their supply of nutrition.

In metronomic chemotherapy, low doses (sometimes only 10% of the MTD) of chemotherapy drugs are given daily (or on a regular basis), at home. At these low doses, the drugs target the lining of the blood vessels feeding the tumor. They stop new tumors from building new blood vessels (angiogenesis). As their supply lines are cut off, the tumors starve. Some tumors simply stop growing, while others actually shrink, as a result of the treatment.

The low doses mean that the normal tissues of the body are rarely affected, and side effects are greatly reduced.

Metronomic chemotherapy is an exciting new approach in oncology. In a recent study of dogs with soft tissue sarcomas (STS), metronomic therapy, using low doses of oral cyclophosphamide and piroxicam, was very effective at preventing tumor recurrence when used after surgery when compared with the standard post-operative radiation treatments.