Cancer Therapies

Chemotherapy

Chemotherapy literally means treatment with chemicals or drugs. This word has become synonymous with cancer chemotherapy in our culture and provokes an immediate emotional response for everyone, stirring up visions of gaunt people with no hair and intractable nausea. While it is true that chemotherapy has side effects, in veterinary medicine most of our patients have side effects that are manageable at home, with less than 10% having side effects that require hospitalization. As compared to human chemotherapy protocols for similar cancers, many veterinary protocols are less intense. Our goal in veterinary oncology is to offer longer life for animal cancer patients, but also to balance that with a good quality of life.

Some common chemotherapy agents used in the treatment of cancer include Adriamycin (generic name doxorubicin), vincristine, Cytoxan (cyclophosphamide), prednisone, cisplatin, carboplatin, and L-asparaginase.

Side effects common to most chemotherapy agents include bone marrow suppression, gastrointestinal (stomach/gut) toxicity, and alopecia (hair loss). Individual agents also have some unique toxicities such as bloody urine with cyclophosphamide (sterile hemorrhagic cystitis), heart toxicity with doxorubicin (dilated cardiomyopathy), and kidney toxicity with cisplatin. Hair loss affects relatively few of our patients. This is because animals’ coats grow to a certain length and then stop. Our hair is susceptible because it is constantly growing. Dogs that have coats that need to be trimmed such as poodles, terrier breeds, and old English sheepdogs, will often lose hair during chemotherapy. Terrier breeds with fluffy, whiskered muzzles often lose their facial hair first. Most dogs will be slow to regrow hair where it has been shaved. Cats also tend not to lose their hair, but often will lose their whiskers. It is possible to start seeing hair loss after the first chemotherapy treatment. Gastrointestinal toxicity generally manifests as nausea, vomiting, and/or diarrhea. This can range from not finishing a meal to profuse vomiting and diarrhea requiring hospitalization to combat dehydration. Occasionally there is blood in the stool. These problems usually occur 3-5 days after the treatment and last 3-5 days. For most drugs, bone marrow suppression is most significant approximately 7-10 days following treatment. The bone marrow rebounds quickly but for a few days the white blood cell counts (and sometimes platelet counts) are lower than normal. This is usually not a clinical problem but if counts are low enough, the body lacks infection-fighting white blood cells and can be susceptible to infections anywhere in the body. This can include life-threatening problems such as pneumonia or blood infection (sepsis).

The reason we see these side effects with many drugs is that chemotherapy tends to target rapidly dividing cells, which is a characteristic of cancer cells. Therefore, cells in the body that normally have a rapid turnover such as the bone marrow or the lining of the stomach and intestine, are also susceptible to injury. Some drugs have unique toxicities that do not occur with other drugs, even with drugs with the same mechanism of action. Adriamycin can cause irreversible heart damage; Cytoxan can cause bloody urine. The incidence of these toxicities is relatively low. Greater than 80% of patients tolerate side effects well enough to be managed at home. Anti-nausea and anti-diarrhea medication can help make our patients feel better during this time. Some patients need to be seen by a doctor but can be treated on an outpatient basis. Less than 10% of patients need to be hospitalized for side effects related to chemotherapy. Most of these patients will get better with prompt and aggressive therapy. It is possible for patients to die of complications of their chemotherapy, even with appropriate treatment, but this is rare. If your pet is undergoing chemotherapy and there are signs of illness, it is important to consult a veterinarian at least by phone initially, even if it is after hours, to help decide if medical attention is recommended.

Overall, most clients are satisfied with their decision to pursue chemotherapy. There are certain cancers in which repeated studies have shown a survival benefit with chemotherapy, such as lymphoma (also called lymphosarcoma, a cancer of one kind of white blood cell), osteosarcoma (primary bone cancer), and hemangiosarcoma (a cancer of the blood vessels, often found in the spleen). There are many other cancers where response to chemotherapy has been promising, and still other cancers where chemotherapy is recommended based on the known behavior of the tumor, despite lack of studies to date to confirm its efficacy. The most important part of deciding if your pet should go through chemotherapy is to first decide your treatment goals. If you want to have as much time with your pet as possible, a more aggressive protocol may be the right decision. If your primary goal is that your pet not experience even a single day of side effects, then a less aggressive approach may be in order. No matter what you decide, if it is right for you and your pet, then it is the right decision. Establish a good basis for trust and communication with your veterinarian and he or she will help guide your decisions. Ask your veterinarian if he or she is comfortable giving chemotherapy and if they are familiar with managing possible side effects, so that if your pet has difficulties, you know what channels to follow. Chemotherapy side effects can be made less severe in some patients with proper medication and supportive care. Along with your veterinarian and their staff, you are a critical member of your pet’s health care team.

Tips for managing chemotherapy side effects at home

Although chemotherapy can cause side effects, there are things you can do to help your pet through the rough spots. It is also important to remember that when your pet doesn’t feel well, it is usually something you can help at home, but not always. Do not hesitate to contact the University of Missouri Veterinary Teaching Hospital or your local veterinarian or animal emergency clinic if any of the following occur at any hour:

-Your pet does not respond to you
-Your pet runs a fever (for dogs this is generally greater than 103°F)
-Your pet vomits or has diarrhea more than 3 times per hour or 3 times per day
-You see blood in your pet’s vomit, stool, or urine
-Your pet just doesn’t seem to be feeling well

Here are some things you can do at home:

-A fever is an emergency and must be treated by a veterinarian
-For stomach upset and diarrhea, initially rest your pet’s stomach by taking all food and water away for a few hours. If vomiting continues during this period more than once, call your veterinarian to see if your pet should be seen.
-Once your pet has stopped vomiting for at least 4 hours, try offering small sips of water frequently and if your pet tolerates this, try small meals frequently (few tablespoons of food every few hours).
-When you offer food, stick to foods that are gentle on the stomach (boiled chicken or hamburger and rice, or a low fat dog food). Avoid treats and high fat foods such as sausage, bacon, or cheese.
-For diarrhea, the same approach is helpful, and you can also give Pepto Bismol® liquid at a dose of 2 to 4 teaspoons up to every 4 hours for 24 hours. If the diarrhea worsens during this time, or your pet feels worse, or if the diarrhea continues at the same rate beyond the 24 hours, then your pet should be seen by a veterinarian.
-There are anti-nausea and anti-diarrhea prescription medications that can be given preventively if your pet has difficulty with nausea and/or diarrhea. Continue to communicate with and work with your oncology team to make the course of chemotherapy as comfortable as possible for both you and your pet.