Cancer is a tissue mass characterized by persistent, excessive, and disorganized cell growth that is unresponsive to normal control mechanisms. Thusly, 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 is 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.

TYPES OF CANCER TREATMENTS

• 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 New England Veterinary Oncology Group (Waltham, Massachusetts), 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.

CANINE AND FELINE LYMPHOMA

Lymphoma is a malignancy (cancer) arising from the lymphoid tissues involving the immune system as well as any organ. When the malignant cells are present in the patient’s bone marrow, causing blood disorders, it is referred to as leukemia. Some patients have multiple sites where malignant lymphocytes can be found. The patient can be staged (assessed for disease) as follows:

• Stage 1: Malignancy involves a single lymph node or single site.
• Stage 2: Involvement of a cluster of lymph nodes in a regional area (including a single tumor of the intestinal tract).
• Stage 3: Involvement of all peripheral lymph nodes.
• Stage 4: Involvement of liver and/or spleen; associated with shorter remissional/survival times.
• Stage 5: Involvement of the bone marrow and peripheral bloodstream; associated with shorter remissional/survival times. Substages: Lymphoma patients can be subdivided into:
• Substage A: Without systemic signs (ie. not ill).
  Substage B: With systemic signs (ie. physically ill).

Staging the cancer patient is vital in determining the best treatment and preparing prognostic information.

T-CELL VS. B-CELL LYMPHOMAS

You may see mention of lymphomas and leukemias as being either of a “B-cell” or “T-cell” origin. A patient’s biopsy tissue can be further tested by a technique called immunohistochemistry. This determines the type of cell of the immune system that the malignant clone arose from. The treatment options are the same for both types of lymphoma but over large numbers of patients, it has been shown that the T-cell lymphomas are generally more aggressive. Overall, patients with T-cell lymphomas achieve remission as often as B-cell lymphoma patients but their remission times can be significantly shorter (though not always).

WHY CHEMOTHERAPY?

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 a rapidly progressive disease, prevent the 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 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.

PROTOCOLS FOR LYMPHOMA

There are many “protocols” or treatment schedules available for canine and feline lymphoma. Unfortunately, there is no 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: These are continually updated as the field of veterinary oncology advances.

Selecting a Protocol
As a general rule, combination chemotherapy is superior to single-agent chemotherapy. There are several areas of consideration when determining a chemotherapy protocol for an individual patient. These include:

Stage of the Patient’s Disease
Willingness/availability of the owner to endure treatment schedule
Client expectations/desires
Financial issues
Response of the patient to the treatment

Care of the cancer patient requires unique skills, expertise, drugs, procedures, philosophies, and supportive care. Each area can be discussed in-depth to assist you in determining what path will be best for your particular circumstances.

Please recognize that veterinary patients usually have a dynamic course to their disease and treatment. Estimates for treatment costs do not include unexpected illness, diagnostics, treatment, or hospitalization. Our health team will strive to provide you and your pet with compassionate care as you take this journey with us.

LIFE FOR CHEMOTHERAPY PATIENTS

Chances are that you, or someone you know, have experienced chemotherapy for the treatment of cancer. 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.

In most animals, hair does not grow continually throughout their lives as it does in people. Some breeds, however, are susceptible to at least some hair loss (especially poodles, sheepdogs, Scotties, and schnauzers). If your pet requires a groomer to trim its hair coat Ð then some hair loss can be anticipated. Pets, however, are not bothered much by this Ð and they seem to enjoy stylish polar-tec jackets as gifts. 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 (1/4 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.

POST-CHEMOTHERAPY REACTIONS/INSTRUCTIONS

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; metoclopramide is most commonly used in dogs; cyproheptadine 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.; “childrenÕs dose” for dogs under 40 lbs., and 1/4 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 depressed, assume your pet requires immediate 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 1/4 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”) is 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: