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Information on this page is courtesy of Bath-Brunswick Veterinary Associates, Inc. from an article by Dr. Gail D. Mason, DVM, MA, DACVIM

 

Many of our patients require far more than routine preventative care. This may include therapy for certain types of cancers. Though there are similarities between human and veterinary cancer treatments, there are some important differences. Improved therapies can provide acceptable options for pets and their owners.

CANCER & CHEMOTHERAPY IN COMPANION ANIMALS

A cancer is a tissue mass characterized by persistent, excessive, and disorganized cell growth that is unresponsive to normal control mechanisms. Cancer is a leading cause of death in dogs and cats. Why this happens, in most cases, is not yet known. As a result of improved owner and veterinary care, pets are living much longer and thus are more susceptible to diseases of old age, such as tumors. Compared to people, dogs develop tumors twice as frequently, but cats only half as frequently. If your pet is thought or known to have cancer, a consultation with a veterinarian experienced in oncology can provide you with valuable information regarding treatment options and expectations.

Terms Used in Cancer Medicine:

Tumor: simply means a "swelling," which may or may not represent cancer.

Benign Tumors: have many normal growth characteristics. They do not "spread" or invade other organs. They, may however, compress body organs or tissues by virtue of their size. Surgical removal is usually curative.

Malignant Tumors: often have rapid, irregular growth characteristics. These tumors can invade normal, local tissues, as well as spread to other tissues (especially the liver and lungs). New tumors can grow at these secondary sites, eventually causing the demise of the patient.

Metastasis: the process whereby a tumor spreads to secondary sites. These new tumors are referred to as ""metastatic"," or "metastases."

Oncology: refers to the study of tumors, including their biological behavior and treatment.

Remission: denotes a decrease in tumor size (often called "tumor burden") over time. Remission time is the length of time in which the tumor is under control. Currently, treatment of cancer in animals can often result in fairly lengthy, good quality remission times. That still means that for many types of cancers, their return is inevitable. This fact must be contemplated and discussed before the client and the veterinarian decide to treat an animal for cancer. Having reasonable and accurate expectations will provide a more positive experience for all those involved.

Surgery: surgical removal of tumors is a very common and valuable approach for solid tissue tumors. It can be used for soft tissue as well as for bone tumors. It can sometimes be curative on its own, if the disease process is localized and detected very early.

Radiotherapy: or "radiation" therapy is available at large veterinary institutions such as Tufts University School of Veterinary Medicine (North Grafton, Massachusetts) and Angell Memorial Animal Hospital (Boston, Massachusetts). It consists of the use of a radioactive beam to damage and/or kill malignant cells in a localized area. It can offer good quality remission times for many types of tumors, but usually not cure. Animals are surprisingly tolerant of radiation therapy.

Chemotherapy: is the use of certain drugs alone, or in combination to control tumor growth. All of the drugs currently given to animals are human anti-cancer drugs. Fortunately, many of the negative consequences of their use in human medicine are not experienced in veterinary medicine. Chemotherapy and/or surgery are the two most important treatment modalities in veterinary cancer medicine. A combination of therapies may also be indicated in certain cancers. Some cancers require a specific, brief number of treatments, while others requiring ongoing treatment to maintain remission.

 
Specific Cancers
Type of Tumor
Type of Treatment
Lymphoma
Chemotherapy (several types available)
Mast Cell Tumors
Chemotherapy, Surgery (+/-radiation)
Fibrosarcomas
Surgical +/-chemotherapy, radiation
Oral Cancers
Surgical, with reconstruction
Mammary Tumors
Surgical (+/-chemotherapy follow-up)
Osteosarcomas (bone)
Surgical + chemotherapy follow-up
Hemangiosarcomas
Surgical + chemotherapy
Skin Tumors
Surgical +/- chemotherapy, radiation
Transitional Cell Carcinomas
Surgical + chemotherapy
Undifferentiated Sarcomas
Surgical +/-chemotherapy, radiation

Because Dr. Gail Mason treats many patients affected withLymphoma or Osteosarcoma, specific discussions on these tumors follow.


 
CANINE AND FELINE LYMPHOMA

The word "chemotherapy" usually evokes unpleasant thoughts in most people's minds. We prefer to think of it as "therapy" for a disease, in the same way people take medications for certain illnesses. The ultimate goal of therapy would be to cure the patient of cancer. In most instances at this point in time in veterinary medicine, this goal is not realistic. The goal we do strive for is to control rapidly progressive disease, prevent spread of the tumor, restore deteriorated function, and provide a good quality of life during the time of remission. The term "remission" means a time interval during which there are no outward signs that the patient has cancer. In the case of lymphoma, if the maximum combination protocol is used, it is expected that 80% or more of patients will go into full remission. The average duration of remission is longer than 12 months. Unfortunately, it is impossible to predict which animals will achieve a full remission or for how long. We do know, however, that if no therapy is used, most pets will die from their disease in a few days to a few weeks.

There are many "protocols" or treatment schedules available for canine and feline lymphoma. Unfortunately, there is not one "key" formula as yet that has been proven superior to all others. Most published protocols contain the same or similar class chemotherapy agents, with minor variations on combination agents and timing of treatments. Most veterinary internists and oncologists use the protocols that they are the most familiar with, and that best fit the particular lifestyle and expectations of the client, and well-being of the patient. A brief synopsis of treatment categories for feline/canine lymphoma is as follows:

 
Regimen
Risk of Side Effects
Expected Remission Time*
Costs
Prednisone (cortisone)
low
2 months
very low
Prednisone + Cytoxan®
low to moderate
2-4 months+
low
COP (Prednisone, Cytoxan®, Vincristine
low to moderate
6-12 months+
moderate
ACOPA Adriamycin®, Cytoxan®, Predisnone, Vincristine, Asparaginase
moderate to high
8-36 months
higher
*NOTE: No guarantee of remission times can be made. These are average lengths. The stage of the disease, protocol selected, general health of the animal, and several other factors are only some of the determinants of remission time.

 
Behavior & Treatment

Osteosarcoma is the most common primary bone tumor of dogs. Large and giant dog breeds are at highest risk of this malignancy. This tumor is locally destructive to normal body tissues, and has a high metastatic rate (tendency to travel to distant sites in the body). It is one of the cancers in dogs that can be painful when it is in its active stages. Bones of the limbs that are affected by osteosarcoma can be weakened to the point of a fracture (called a pathological fracture).

If no treatment is rendered, the animal usually succumbs to the disease within 1-2 months from the time of diagnosis. Surgical resection of the tumor and/or limb amputation are key to treatment of osteosarcoma. Though many owners are at first hesitant about surgery, they frequently observe that their dogs improve dramatically after this treatment. This is by and large because a source of constant pain has been removed. It is important to note, however, that surgical resection alone does little to prolong the dog's survival time.

What about chemotherapy?

Osteosarcoma is always considered to have spread microscopically in the dog's body by the time the diagnosis is made. This is the reason that surgery alone fails to control the disease. To attack the cancer cells both locally and systemically, chemotherapeutic agents can be used. The goals of therapy are to preserve a good to excellent quality of life for the dog, eliminate pain, and provide as long a remission time as is possible. Cure is not a reasonable goal at this time, and this fact must be realized by the owner prior to initiating therapy.The two most common chemotherapy agents used for osteosarcoma are Adriamycin® and platinum compounds such as Carboplatin or Cisplatin. Because Adriamycin® and Carboplatin are synergistic with respect to their anti-cancer activity, they are often alternated in treatment protocols. Treatments are done as outpatient visits, every 3-4 weeks, for a total of 4-6 treatments. The actual treatment time takes approximately 30 minutes.

As previously mentioned, a dog that is given no treatment, or treatment with surgery alone is expected to live 1-2 months from the time of diagnosis. However, for a dog that undergoes surgery plus adjunct chemotherapy, the expected 1 year survival rate is 50%, the 2 year survival rate falls to about 20%. The cancer eventually starts to grow in the lungs which leads to coughing, weight loss, and malaise.

Side Effects of Therapy?

Healing from surgery is usually rapid and complete. The results in terms of cosmetics, function, and owner acceptance is excellent in most cases. All chemotherapeutic agents have potential side effects, which should be understood by the owner so that proper intervention can occur if the need arises.

Adriamycin®

Adriamycin is a potent anti-cancer drug used in both humans and animals for many different types of cancers. It has been shown to be beneficial in treating canine osteosarcoma, but is best used with a platinum compound. Occasionally, nausea and vomiting can occur within 2 days of administration of the drug. These episodes are infrequent and can usually be mitigated by using anti-nausea medications. The most serious side effect results from the dog's white blood cells being lowered (infection fighting cells). This usually occurs about 5-8 days after treatment. Symptoms include sudden lethargy, refusal to eat, reluctance to rise, and fever. If this happens, follow the directions you have been given and/or call the hospital ASAP. This side effect can be rapidly and successfully treated. However, ignoring these important signs can be lethal!

Carboplatin

Carboplatin is the "gold standard" in treating canine osteosarcoma. It is useful as a single agent, or in combination with Adriamycin®. Carboplatin occasionally causes dogs to act "subdued" or have a decreased appetite for 2-3 days after administration. This effect tends to be mild. Carboplatin, like Adriamycin®, has a tendency to lower the white blood cell/platelet counts. This is less common and usually less severe than with Adriamycin®. It occurs approximately 10-13 days after administration. This drug could theoretically cause damage to the kidneys over time, but this is very uncommon. Your dog will be monitored for side effects during treatment. Unfortunately, because the "platinum" compounds actually do contain platinum, they are very costly! A cost estimate of treatment will be given to you during your visit.

Quality of life?

Fortunately, most dogs who undergo treatment for osteosarcoma are lucky enough to have an excellent quality of life! They are pain free, and done with treatment after 4-6 rounds (3 week intervals). They rarely have to be hospitalized, so that they can be at home with "their people." Dogs can continue to do virtually every activity that they are used to doing (yes, even hiking..). We hope to make your dog's remission as long and enjoyable as possible!

What is Life Like for Chemotherapy Patients?

Veterinarians who treat animals for cancer use many of the same chemotherapy agents that human oncologists use. Yet, in many ways the experience for pets seems very different. Why? For one thing, dosages of chemotherapy agents used in animals tend to be much lower than those used in people. Humans are given the highest doses possible, the consequences of which may require bone marrow transplantation, extended hospitalization, and numerous costly medications - all with good cause. However, for veterinary patients, this process would be unacceptable and cost prohibitive for most owners. The general quality of life for many veterinary cancer treatment patients can be surprisingly good and very close to normal. Most of the time they can maintain their normal activities, travel, and have fun with the families that love and care for them.

Most currently used anti-cancer agents do not specifically target cancer cells. Rather, they target and damage or kill rapidly growing cells. For the patient, this means cells lining the stomach and intestine (high turnover rate), cells of the bone marrow that make up the immune system (white blood cells, in particular), and cancer cells. It then is little surprise that the most common side effects of chemotherapy agents include mild to moderate nausea, vomiting, diarrhea, and increased risk of infection. Hair loss, in contrast to humans, is uncommon in dogs and cats on chemotherapy. The good news is that the normal cell lines can almost always regenerate themselves, while the less well organized malignant cells suffer great damage. However, even at higher dosages, microscopic malignant cell clones remain alive, albeit dormant in the body. Eventually these give rise to drug-resistant cell lines. This is the biological basis of recurrent or metastatic cancers.

It is not a "given" that untoward side-effects will occur in any one patient. In fact, the majority of our patients complete their therapies without major complications. If they do occur, however, you should be prepared to recognize them and take appropriate action. Over time, the tendency is to have less frequent side effects, as the individual animal's sensitivity to the drug agents become known, the treatments are less frequent, and the cancer is in remission.

Risks to People Living with Chemotherapy-treated Pets

The anti-cancer drugs are excreted from the animal's body via urine and feces. This usually happens in the 48 hours following treatment, but can be as long as 5 days for Adriamycin®. If it is possible, you should try to have the animal eliminate in an area away from the immediate yard or play area. Cat boxes should be changed regularly, and waste material handled with a scoop. If urine or feces must be handled, use heavy rubber or latex gloves and disposable wipes/towels. Place all waste/towels in a plastic bag and seal it, before disposal. Smooth surfaces may be washed with a dilute bleach solution (¼ c. to 1 gallon of water). Humans and other household pets living with treated pets are generally thought not to be at any health risk, just as in the case with humans. Pregnant women should not handle ANY animal waste or anti-cancer medications. If any family member living with the pet has a condition that would suppress his/her immune system, it would be prudent to let the veterinarian know.

Gastrointestinal Side Effects

Nausea (and refusal to eat) can occur in veterinary patients, and seems to occur more frequently in cats than in dogs. If this happens 1-3 days post-treatment, it is usually transient and requires no specific treatment. Tempting the pet with favorite foods, and warming the foods slightly will often increase palatability. For dogs, adding cooked eggs, pasta, lean chicken, or hamburger can be helpful. If this condition persists, medication to reduce nausea and promote appetite can be used; Reglan® is most commonly used in dogs; Periactin® for cats.

Vomiting can also occur at any time during treatment. When it occurs 1-2 days post-treatment, and the pet is otherwise bright, active, and alert you can use Pepto Bismol® using the label "adult dose" for dogs over 40 lbs.; "children's dose" for dogs under 40 lbs., and ¼ tsp. for cats (dosed up to twice daily). Remove food for 12-24 hours, and replace it with a pile of ice in a dish. This will help to maintain hydration without stimulating further vomiting. If the vomiting is repetitive (greater than 4X), contains blood, or the pet seems weak and/or depressed, your pet probably requires veterinary attention.

Diarrhea may occur, but is often mild and transient. Several over-the-counter treatments may be given safely to pets and may reduce intestinal discomfort. Imodium A-D® or Kaopectate® is dosed at "adult dose" for dogs 40 lbs. and over; "children's dose" for dogs less than 40 lbs.; and ¼ tsp. for cats up to 2-3X daily. If the diarrhea is severe, persistent, contains blood, or the animal seems weak or depressed, veterinary attention is required.

Fever/Sepsis As previously mentioned, virtually all chemotherapeutic drugs have the ability to at least temporarily suppress the body's own immune system. The normal range of white blood cell counts in animals is about 6,000-17,000/cmm. If the white blood cell count (neutrophils or "wbcs") are below about 2,000, then the pet runs the risk of systemic infection. The pet will usually manifest fever (but not always). If the bacteria travel through the bloodstream, it is known as "sepsis." In rare cases, shock can occur (septic shock), and without rapid treatment, the risk of death is high. Though this period of susceptibility is brief, and occurs at a fairly predictable time, its consequences can be life-threatening. Below is a list of the most commonly used drugs and the expected low point in cell counts (the "nadir"), given in days post-treatment:

 
Drug
High Risk Period
Adriamycin® (doxorubicin)
7-10 days
Vinblastine
< 7 days
Cytoxan® (cyclophosphamide)
7-10 days
Lomustine (CeeNu®)
7 days, then again at 21 days
Mitoxantrone
7-10 days
Carboplatin
10-13 days
Signs of Fever or Sepsis
  • fever > 103F (temperature taken by rectal thermometer should be between 100 and 102.8F.
  • extreme lethargy (refusal to get up off of dog bed, etc.)
  • complete disinterest in food
  • extreme weakness
  • pale and somewhat "sticky" gums
  • severe vomiting/diarrhea
  • Immediate action is necessary.
  • Start the antibiotics you have been given; double the first dose, then continue as label directs.
  • Track the temperature at hourly intervals.
  • If pet is not significantly better in 1-2 hours, call your local veterinarian or Bath-Brunswick Veterinary immediately. DO NOT WAIT OVERNIGHT!. This situation can be treated rapidly and almost always successfully. However, an extended delay before initiation of treatment may result in health complications or even death. Your local veterinarian has been given treatment protocols for this situation and in most cases this will be more convenient for you. However, our hospital will see this type of emergency AT ANY TIME.
Care & Feeding of The Veterinary Cancer Patient

One of the most important goals of cancer treatment in animals is to maintain as much of the pet's normal lifestyle as possible. This can often mean that once a pet has recovered from cancer surgery, and/or passed the induction (initial) phase of chemotherapy, restrictions on activities are very few, and will be discussed by your veterinarian. For patients with lymphoma, prednisone is usually administered every other day throughout the entire treatment period. In cats, prednisone is given daily. Cancer patients may be more easily fatigued with strenuous activity, so moderation is best. Daily walks and "playtime" are encouraged. Many pets will actually gain weight during therapy and this should be monitored. Obesity increases the pet's risk of concurrent disease, and should be avoided.

It is now known that cancer results in significant alterations in carbohydrate, protein, and lipid metabolism. Fortunately, research findings by Dr. Gregory Ogilvie and others at Colorado State University's Comparative Oncology Unit have lead to the creation of a specific dietary program which depletes cancer cells of their required nutrients. It has been demonstrated that Hill's Prescription n/d diet 1.) increased survival times of dogs receiving chemotherapy treatment; 2.) reduced painful side effects of radiation therapy; 3.) produced statistically longer remission times; and 4.) counteracted many cancer-induced metabolic side effects in veterinary patients. The diet is comprised of limited quantities of simple sugars, modest amounts of complex sugars, modest amounts of highly digestible proteins, and calculated amounts of certain types of fat (including n-3 fatty acids which have a negative effect on tumor growth, and improve survival times). This diet and others that will follow, help improve the quality and quantity of life for the veterinary cancer patient!

**Information from Ogilvie, Gregory and Davenport, Deborah. From Canine Cancer, Information released by Hill's Pet Nutrition, Inc. and The Morris Animal Foundation (1998).

Drug Dosages

Chemotherapy treads a narrow path between effectiveness and toxicity. In fact, chemotherapeutic protocols are most often limited not by the ability of drugs to kill tumor cells, but by their toxicity to the patient. The goal is to destroy as many malignant cells as possible while leaving enough normal, "organized" cells to recover organ function. It is important, therefore, that we use the highest dosages that we think the patient can tolerate. The more cancer cells surviving any one time, the sooner the patient will become resistant to the beneficial effects of the drugs.

Visits and Costs

For a cancer such as lymphoma, therapy involves a significant time commitment on the part of the owner/family. Outpatient visits are generally once weekly for 4 weeks, then every 3 weeks for up to 18 months. However, we make every effort to accommodate the owner's schedule, and most visits require 20 to 30 minutes. Many clients like to leave their pet with us temporarily while they go do errands, and you are welcome to do this. You may halt therapy at any time, but we like to have the owner commit to at least 4 weeks, so you will have the benefit of seeing how well a pet can do. Due to the new OSHA hazard laws, and the fact that the animal must make no movement during the intravenous injections, we regret that it is not feasible to have the owner present during the few minutes of chemotherapy injections. Rest assured that your pet will be gently and expertly restrained by the oncology technician and the doctor. Relative to most other treatments in veterinary medicine, chemotherapy is a costly service to provide. The costs reflect the professional time and expertise required, the high costs of chemotherapy agents (the same used by humans), the special equipment and personnel protection required, and the removal of biomedical hazard waste. Realize however, that this therapy is unique in that it can successfully prolong an animal's life!

Is It Worth It?

This is a difficult question for us to answer. Every situation and client-pet relationship is different and must be dealt with individually. If it were ever obvious that therapy was not working, or that the pet was indeed experiencing pain or discomfort, we are ethically obligated to inform you. What we can say is that most pets do indeed appear to enjoy their extended life period and do not even realize that they are "ill." However, the owner(s) must believe that they are doing the right thing for their pet, for their situation.

Prednisone is the least toxic of all the chemotherapy agents. It is not a specific chemotherapy drug, and has many different uses in medicine. It is usually well tolerated by pets. It commonly causes increased thirst, urinations, and appetite. It can have irritating effects on the stomach lining.

Elspar© (Asparaginase) is also well tolerated. In rare instances, it can cause vomiting due to pancreatitis. Since it is a protein, there is a (rare) possibility that an animal can have an allergic reaction to it. We would ask that your pet remain in the lobby for about 15 minutes after this injection.

Vincristine© has little tendency to make an animal ill. Occasionally, there will be 1 or 2 episodes of "innocuous" vomiting 24 hours after the injection, which disappears without treatment. It is very irritating to the surrounding tissues if it leaks from the vein at the injection site. If you notice any inflammation where the injection was given, notify the doctor.

Cytoxan© is a potent chemotherapeutic agent and can lower the white blood cell count about 7 days after it is given. The tablets should be given in the morning (all at once with food), and the pet should be given ample opportunity to empty his bladder throughout the day. Occasionally, bloody urine can occur due to bladder effects. If this occurs, call the doctor and the medication can be changed. If your pet should get sick about 1 week post treatment, follow the instructions on the owner's sheet given at the start of treatment.

Adriamycin© is the most potent of the agents, and like Cytoxan©, can lower the white blood cell count. Mild nausea can occur, and the adult dose of Pepto Bismol® can be given as directed on the label. If there is irritation at the injection sites, notify the doctor. Long term effects can involve the heart, but our protocols have been calculated to lower this risk. If your pet gets ill about 1 week after therapy, follow the instructions on the owner's sheet.

Most of the drugs are excreted in the urine within about 48 hours after administration. It would be wise to walk your pet away from his usual elimination spots (in a more out-of-the-way spot) for those two days. If he does urinate in the house, the urine should be promptly cleaned up, and the owner should wear latex gloves so no direct contact is made. You are in no danger living with an animal on chemotherapy, but it is prudent to avoid human exposure to these drugs when we can. You will be instructed to wear latex gloves, for your protection, while giving certain medications.

All textual materials above copyright (c) 2000 Bath-Brunswick Veterinary Associates, Inc.

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