Cancer begins as a biologically abnormal change in a single cell in one ofyour pet's organs. This cell divides repeatedly, producing more abnormal cells.These new cells also divide at an extremely rapid rate and cannot be stopped byyour cat's normal internal monitoring system, which makes normal cells behave.These abnormal cells are biologically destructive: they form solid tumors and in-vade and destroy surrounding tissue. Malignant tumors produce chemical sub-stances that aid the cellular destruction and help stimulate a blood supply (toobtain oxygen and nutrition) for the tumors. Malignant cells frequently spreadthroughout the body by way of veins or lymph vessels and thus bring their destruc-tive ways to other organs in your cat's body. This process is called metastasis.
WHAT IS CANCER?
Why should normal cells in your cat's body suddenly transform into malignant cells? Researchers feel that cancer is caused by one or more of the followingfactors: contact with harmful environmental agents, heredity, viruses, immunologicfactors, or body hormones.
Harmful Environmental Agents
Chemical carcinogens (agents that produce cancer) are being identified in ourair. water, and food. Our pets share this unhealthy environment and share the car-cinogens, most of which alter cellular genetic material. Asbestos workers and cig-arette smokers have a high incidence of lung cancer. Since cats don't smoke anddon't work - especially around asbestos they have a very low incidence of lungcancer. However, white cats that are excessively exposed to sunshine have a highincidence of skin cancer, just as do fair-skinned humans.
Heredity
Certain breeds seem to have a predisposition for and a high incidence ofspecific cancers.
Viruses
Tumor-causing viruses are being identified. These viruses change the geneticcode in cells, transforming them into malignant cells. The most publicized cancer-inducing virus is the feline leukemia virus.
Immunologic Factors
Tumor cells have antigens on their surfaces. Your cat's immunesystem (antibodies, lymphocytes, and macrophages) recognizes these "foreign"cells and attempts to destroy them. It has been speculated that our pets (and ourbodies) produce cancer cells quite often but the immunologic defenses in healthyhumans and cats destroy these cells before they can get established. This is calledimmunologic surveillance. If the immune system fails for any reason, the cancercells can start their destruction.
Body Hormones
Although it has not been established empirically, having an ovariohysterec-tomy for your cat before her first heat may help avert breast cancer in later years.
Cancer will be prevented only when we understand how and why these fac-tors cause normal cells to transform into cancer cells. For example, if air pollutionand smoking induce lung cancer in humans, why don't all exposed humans developcancer?
If your pet develops cancer, don't feel that all is hopeless. In many cases,modern veterinary medicine, just like human medicine, has therapy available tohelp your pet. The chance for a cure or remission will depend on the type of tumor,its location(s), the type of therapy used, and your cat's general health (for example,whether general anesthesia or chemotherapy can be tolerated).
First, you and your doctor must be sure that your cat has cancer. Most typesof cancer cannot be diagnosed by looking at your pet. Some of the signs, such asloss of appetite, gradual weight loss, weakness, lumps in the abdomen, and evenugly skin growths, could indicate a simpler problem. Your doctor must performcertain tests and take radiographs to verify that cancer is present, to determine thetype and extent of the cancer, and to decide on the best type of treatment, if any,for the malignancy. Your veterinarian may select some or all of these diagnostictools to give you clear assessment of your cat's situation.
Once the lab tests and X-rays have been studied, the doctor can determinethe next step. If there is cancer and it is treatable, you should receive the followinginformation so that you and your doctor can reach a common understanding anddecision in your cat's best interest.
- What are the chances for a cure or remission?
- If we can expect a remission, how much time does this give my cat to livefree of pain and discomfort?
- What type of therapy will be used?
- What are the side effects of the therapy?
- What is the cost of the therapy?
- How much of my time will be taken up by visits to the veterinary hospitalfor therapy and follow-up exams?
- Is there any new cancer therapy that will not cause my cat discomfort andthat may benefit it and contribute to current human cancer studies?
THERAPY
At the present time, there are five modes of therapy, effective either singly orin combination, used to treat various cancers in different stages of development:surgery, chemotherapy, radiation therapy, cryosurgery, and immunotherapy.
Surgery
This is the major method to diagnose and treat cancer. The major drawbackis that a microscopic number of tumor cells that may be left behind can spreadand cause a relapse. If there is a high risk of relapse, or if the entire tumor cannotbe successfully removed, one or more of the other modes of therapy may also be used.
Chemotherapy
The hope of chemotherapy is in using a drug or chemical agent that will killtumor cells while doing as little damage as possible to your cat's healthy cells. Thedrawbacks of chemotherapy are its expense (unless the therapy is supported bygovernmental grants to a university or private veterinary medical center) and thepotential toxic effects on healthy tissue.
Radiation Therapy
Radiation therapy is an important and effective mode of cancer treatment inhuman medicine. It is now being recognized as an important form of general cancertherapy. Unfortunately, the cost of the equipment and facilities has limited its useto university and private veterinary medical centers.
The cells of certain tumors seem to be more susceptible to therapeutic dosesof ionizing radiation. These ions seem to kill tumor cells by disrupting their "code of life" the DNA and chromosomes. The cells die when their attempt at divisionis ineffective. Susceptible tumors are termed radiosensitive.
Cryosurgery
Certain tumors especially some skin and mouth tumors have been suc-cessfully treated with cryosurgery. This is a technique using liquid nitrogen or acompressed gas such as nitrous oxide to kill tumor cells by alternately freezingand thawing the tissue. A temporary but odorous and oozing wound is the maindisadvantage until healing occurs.
Immunotherapy
A new form of therapy that seems to hold some promise, especially whencombined with surgical treatment, is immunotherapy. Your own and your pet'simmune system protects the body against "foreign" cells such as bacteria, viruses,and tumor cells. In cancer, the immune system is suppressed or blocked from de-stroying the tumor cells. Certain biological and chemical substances called im-mune adjuvants are being used to stimulate the immune system in hopes of gettingremissions in breast cancer.
Early diagnosis and treatment are most important if therapy is to be successful. If your cat is over five years old and you suspect the presence of cancer, seeyour veterinarian.
Most cat owners are willing to prolong their pet's life if it will be free of painand suffering. If you and your veterinarian reach an understanding that this is notpossible, it is in your pet's best interest to administer euthanasia. In this way, pets do not have to suffer through the pain and misery of cancer that hasspread throughout the body. But please consider euthanasia only as one option.Just like heart disease, cancer can be considered a chronic illness that can, in manycases, be controlled - that is, your cat can live free of pain and discomfort. Eutha-nasia should be used only if treatment has failed or if your cat has a form of cancerthat is completely hopeless.
Skin cancer, lymphosarcoma, and breast cancer are three forms of cancercommonly seen in cats.
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