Chemotherapy

Chemotherapy is the use of certain drugs alone, or in combination to control tumour growth. But for many people, the word "chemotherapy" brings to mind negative associations -- particularly debilitating side effects. So it?s not surprising when they shy away from treating their pets with chemotherapy. But most animals do not suffer the kinds of side effects that humans do for a variety of reasons, including:

smaller doses are given less often
animals don't have the psychological hurdles to overcome that we do

The important question to answer for any pet with cancer is "What is a realistic goal of treating this animal with chemotherapy?" In veterinary medicine, the goals we strive for are to:

control rapidly progressive disease
prevent spread of the tumour
restore deteriorated function
provide a good quality of life during the time of remission

For a cancer such as lymphoma, therapy involves a significant time commitment on the part of the owner and family. For dogs, visits for chemotherapy are needed once weekly for 6 weeks, then every 2 weeks for 6 additional treatments, and finish with 4 weekly treatments. In most cats there are also 6 initial weekly treatments, after which treatments are continued every 2 weeks for a total of 12 months. We generally recommend overnight hospitalization after the first chemotherapy treatment in both cats and dogs receiving treatment for lymphoma. After this, animals are admitted as day-patients; many owners find it most convenient to drop their pet off on their way to work in the morning, and pick them up on their way home. However, we make every effort to accommodate the owner's schedule. While you have the option to halt therapy at any time, it is important to remember that it will take at least 3 to 4 weeks for some animals to enjoy the benefits of chemotherapy.

All of the drugs currently given to animals are human anti-cancer drugs.

Chemotherapy drugs work by targeting and damaging or killing rapidly growing cells. For the patient, this means cells lining the stomach and intestine (high turnover rate), and cells of the bone marrow that make up the immune system (white blood cells, in particular), as well as cancer cells. These medications are extremely potent, and must be carefully chosen on a case by case basis. Considerable expertise is needed to choose the most appropriate drugs, dosages and treatment protocol for each individual patient. Veterinarians that are board certified in medical oncology have specialized knowledge that is vital in making these critical decisions.

Most patients complete their course of cancer therapy without major complications.

Side effects tend to decrease in severity over time, as the unique drug sensitivities of each animal become better defined, as treatments are given less frequently, and once the cancer is in remission. Owners can be reassured that the most common side effects should be mild to moderate and may include decreased appetite, nausea, vomiting, diarrhea, and increased risk of infection caused by bone marrow suppression. Hair loss is uncommon in cats and most dogs on chemotherapy, although certain breeds such as terriers and poodles may experience more significant hair loss.

Normal cell populations, such as those in the intestine or bone marrow, can almost always regenerate themselves. This means that most chemotherapy-related complications that occur in these tissues resolve relatively quickly. At the same time, the less well organized malignant cells will suffer greater damage and have a decreased ability to repair themselves. However, even after treatment using higher doses of chemotherapy, microscopic clusters of malignant cells remain dormant but alive in the body, and will eventually give rise to drug-resistant cell lines. This is how malignant cancers recur and metastasize, and this is why many cancers that are very treatable with chemotherapy cannot necessarily be cured.

Managing side effects

While animals rarely experience severe chemotherapy side effects the way people do, some patients have transient symptoms that can be frightening and upsetting if you are unsure what is causing them or what you should do. Fortunately, simple strategies and treatments usually allow you to successfully manage these complications at home.

Chemotherapy drugs are excreted from the animal's body in the urine and feces, usually within 72 hours following treatment, although it may be as long as 5 days for doxorubicin. Drug residues may also be present in other body fluids, such as vomit. We recommend that you try to have your pet urinate and defecate in an area away from the immediate yard, and especially play areas. Cat boxes should be changed regularly, and waste material handled with a scoop. If urine, feces or vomit must be handled, use heavy rubber or latex gloves and disposable wipes and towels. Place all waste and contaminated wipes and towels in a plastic bag and seal it before disposal. Smooth surfaces may be washed with a dilute bleach solution (1/4 c. to 1 gallon of water). People and other household pets living with treated pets are generally thought not to be at any health risk. However, women who are pregnant or trying to become pregnant should not handle ANY animal waste or chemotherapy drugs. In addition, if any family member living with a pet undergoing chemotherapy has a condition that causes suppression of the immune system, it is important to discuss this with the cancer care team at WVCC as well as the physician caring for this person.

Virtually all chemotherapy drugs have the ability to at least temporarily suppress the immune system. This can lead to serious infections that may be life-threatening if they are not properly treated.

Signs of Fever or Sepsis

Fever of 39.5oC or more (temperature taken by rectal thermometer should be between 37.5 and 39.5oC in both dogs and cats)
Lethargy and weakness (refusal to get out of bed or reluctance to go on walks, etc.)
Disinterest in food
Vomiting
Diarrhea

Nausea (and refusal to eat) can occur in both cats and dogs. Symptoms are usually seen 24 to 72 hours after treatment and include poor appetite, turning away from food when it is offered, and sometimes drooling. This problem is typically transient and requires no specific treatment in many cases. In other situations, anti-nausea medications are indicated and can also be administered prior to future treatments to prevent recurrent problems. Owners can try tempting their pet with highly palatable foods, as well as warming the foods slightly. Bland, relatively low fat foods such as cooked chicken or turkey breast with all fat and skin removed, or very lean boiled and drained hamburger are best. However, cats and dogs that refuse to eat after chemotherapy should not be force fed: this can result in permanent food aversions.

Vomiting can also occur during chemotherapy. When it occurs within 24 to 48 hours of treatment and the pet is otherwise bright, active and does not have a fever, maropitant citrate (Cerenia?) is usually prescribed.

Another effective strategy that can be used either alone or along with anti-nausea medications is to remove your pet?s food, and replace it with a pile of ice chips in a dish. As long as your pet eats the ice, this will help to maintain hydration without stimulating further vomiting. If there has been no vomiting for 12 to 24 hours, you can gradually return your pet to a bland, easily digestible diet. However, if your pet refuses to eat the ice, the vomiting is repetitive (more than 3 or 4 times), contains blood, or your pet seems weak, depressed or has a fever, you should seek veterinary attention.

Diarrhea may occur after chemotherapy in dogs, but is often mild and transient. Diarrhea is rare in cats. Some over-the-counter human treatments may be given safely to pets and may reduce intestinal discomfort, but you should never give a human medication to your cat or dog without first consulting a veterinarian. Cats in particular are very sensitive to many human medications including aspirin and acetominophen, and can develop life-threatening complications if they are used.

Kaopectate(R) may be given to dogs (not cats) at a dose of 1 to 2 cc's per kilogram body weight every 4 to 6 hours, for no more than 48 hours. Pepto-Bismol? regular strength liquid can be given to dogs (but not cats) at a dose of 1 to 2 cc's per kilogram body weight every 6 to 8 hours for no more than 48 hours. Pepto-Bismol? regular strength tablets can also be used in dogs (again, not cats) at a dose of 1/2 tablet per 10 kilograms body weight every 6 to 8 hours for no more than 48 hours.

If the diarrhea is severe, persists for longer than 48 hours with or without medication, contains blood, the animal seems weak or depressed or has a fever, veterinary attention is indicated.

DO NOT WAIT OVERNIGHT! Call us at WVCC immediately. This situation can be treated rapidly and almost always successfully, but appropriate antibiotic therapy is absolutely essential. An extended delay before initiation of treatment may result in health complications or even death. Your local veterinarian will also have treatment protocols for this situation and in some cases this will be more convenient for you. However, the Western Veterinary Specialist and Emergency Centre will see this type of emergency ON ANY DAY AND AT ANY TIME.

Lymphoma

Two of the cancers most commonly, and successfully treated with chemotherapy at the Western Veterinary Cancer Centre are lymphoma and canine osteosarcoma. Lymphoma is one of the most common malignancies diagnosed in dogs and cats. This tumour arises from lymphocytes, and may occur in virtually any organ or tissue. However, dogs with lymphoma usually have dramatic lymph node enlargement, while lymphoma most often occurs in the gastrointestinal tract in the cat. Lymphoma is almost always a systemic cancer, with each patient having multiple sites of involvement throughout the body. Besides lymph nodes and the gastrointestinal tract, other organs that are commonly involved include the liver, the spleen, and the bone marrow. Although complete cures are rarely achieved, treatment of lymphoma with chemotherapy is frequently very successful. There are many "protocols" or treatment schedules available for canine and feline lymphoma, although no single protocol has as yet been proven superior to all others. Most veterinary oncologists choose treatment protocols based on the strength of the published evidence of their effectiveness, how likely they are to preserve the well-being of the patient, and what fits best with your lifestyle and expectations.

Canine Osteosarcoma:

Osteosarcoma is the most common primary bone tumour of dogs. Large and giant dog breeds are at highest risk to develop this malignancy. This tumour is locally destructive to surrounding normal tissues, and has a high metastatic rate (tendency to travel to distant sites in the body). It is typically quite painful when it is actively growing within a bone. Bones of the limbs that are infiltrated by osteosarcoma can be weakened to the point of a fracture (called a pathological fracture).

Fortunately, most dogs that undergo amputation for osteosarcoma improve dramatically because a source of constant, severe pain has been removed. However, surgical resection alone does not prolong the dog's survival time for more than 3 to 4 months, since osteosarcoma has almost always spread microscopically in the dog's body (usually to the lungs) by the time the diagnosis is made. We strongly recommend post-surgical chemotherapy to treat these metastases, and ensure as long a remission time as possible. Four to six doses of chemotherapy are given at 3 week intervals. Although they are not cured of their cancer, dogs receiving postoperative chemotherapy for osteosarcoma have an average survival time of 12 months, and 25% of dogs live 2 years or longer. Hospitalization for treatment-related toxicity is rare, and most dogs are lucky enough to have an excellent, pain-free quality of life at home with their family doing virtually all of the things they enjoy. Without treatment, dogs with osteosarcoma usually succumb to their disease within 1-2 months from the time of diagnosis.

Remission vs. cure

"Remission" is not a cure. It is a time interval during which there are no outward signs that the patient has cancer. Considering the relative life span of animals, increasing the period in which they can enjoy a good quality of life - for months or even years - is significant. For example, in the case of canine lymphoma: 80% or more of dogs are expected to go into full remission, and the average overall survival time is approximately 12 months. Unfortunately, it is impossible to predict which dogs will achieve a full remission or for how long. We do know, however, that if no therapy is used, most dogs will die from their disease in a few weeks.