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 veterinary oncologist 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.

Treatment of cancer in animals often results in fairly lengthy, good-quality remission times. For many types of cancers, their return is inevitable. This fact must be contemplated and discussed before you and the veterinarian decide to treat your 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 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. 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.

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.

Outcomes depend on the:

• Willingness/availability of the owner to commit for the treatment schedule
• Client expectations/desires
• Cost of the treatment
• Response of the patient to the treatment

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

Patients usually have a dynamic course to their disease and treatment. Estimates for treatment costs do not include treatment for unexpected illness, chemotherapy, or hospitalization. Our oncology 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, has experienced chemotherapy for the treatment of cancer. Veterinary oncologists 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.

Although new treatment options are on the near horizon, most current 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. Side effects, however, you should be prepared to recognize them and take appropriate action. Over time, side effects tend to become less frequent as the individual animal’s sensitivity to the drug agents is better understood, treatments are less frequent, and when 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. 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.

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.