Cancer in pets – Part 2 of 2
The treatment of cancer in pets has become a significant part of the therapy provided by veterinarians to keep our pet population healthy and thriving. Depending on the modality used, the type and extent of cancer treated, and the size and the nature of the animal involved, cancer treatment can be very expensive. Therefore, as with any disease, the principle of prevention is better than cure holds true. Not all cancers can be prevented but there are certain types of cancers which can be prevented and others that, if treated early on, require much less invasive treatment and therapy, than cancers which are left to develop.
To understand the treatment and prevention of cancer better, one has to look at what causes cancer. Cancer is derived from the Latin and Greek word “carcinos” which means crab or crayfish. This name comes from the appearance of the cut surface of a solid malignant tumour, where the blood vessels that grow around the tumour looks like the legs of a crab which stretches out on all sides of the body of the crab. Cancer refers to an unregulated growth of cells of the body which can be brought about by a number of causes. These causes include well-known and described external causes like infections, exposure to certain chemical substances like tobacco and environmental pollutants, radiation like excessive exposure to sunlight which causes many skin cancers and poor and incorrect diet and obesity. Lesser known causes of cancer include internal causes and more poorly understood causes like hereditary proneness. External and internal causes agitate the cells of the body which can combine with existing genetic faults within cells that cause them to start growing uncontrollably. For a cell to transform from a normal cell to a cancer cell the genetic material inside the cell which regulates cell growth and differentiation is altered. External agents are often referred to as carcinogens or cancer inducing agents. These agents have the ability to change the DNA of the cells they come into contact with causing them to mutate and change character and nature, which in turn leads to these cells becoming cancerous and spread. A good example of such an agent is tobacco. Human doctors have for years warned people against the dangers of tobacco smoke because it is a well-known fact that it causes many types of cancers, most notably lung cancer.
In most cases of cancer in animals it is very difficult to prove what caused the cancer in the first instance because there can be a combination of causes. Having said that, we know that with certain types of cancer the main culprits can be identified and, if avoided, can help to prevent cancer right from the start. A good example is cancer of the skin, like the ears of white cats or the unpigmented skin of the stomach area of dogs with short coats, called squamous cell carcinoma. This type of cancer can be prevented by daily applying sunscreen on the affected parts of the body (before any cancer starts), or alternatively putting a “sunbathing suit” on for dogs, or best of all, keeping them indoors during the part of the day when the sun causes the most harm (usually between 08h00 and 16h00). Any method used to prevent prolonged exposure to the harmful ultraviolet rays of the sun, will reduce these types of cancer.
Hormones have been proven to be significant contributors to cancer in humans and animals. Fortunately the cancers which come about as a result of reproductive hormones can be significantly reduced in animals by sterilisation. Bitches that aren’t sterilised produce extremely high levels of oestrogen and progesterone when they come on heat twice or three times a year. Over the years the body’s exposure to these high levels of hormones predisposes these animals to cancer of the mammary glands as well as severe, potentially life threatening, uterine infections. It is well documented that having an animal sterilised by removing the ovaries and uterus surgically (ovariohysterectomy commonly referred to as a spay) at a young age (before one year of age), significantly reduces the occurrence of mammary tumours later on in life. Similarly the incidence of prostatic growths and testicular cancer in male dogs are significantly reduced and even eliminated by castrating (surgically removing the testicles) of such animals at a young age.
The incidence of cancer in animals which are physically inactive and obese is also higher as a result of a weaker immune system and negative effects on the endocrine system. The endocrine system refers to many different glands in the body which ranges from small glands in the brain and abdomen like the adrenal gland, to larger glands like the pancreas. These glands secrete different kinds of hormones, which maintain the body’s different functions. Taking your dog for a regular walk or run, will not only have mental and physical health benefits for both of you, but may actually assist in preventing cancer.
Diet forms such an important part of general health and well-being in pets that the prevention of cancer by feeding a properly formulated diet goes almost unnoticed. In humans the incidence of cancer from eating the wrong foods can be as high as 20%. For humans eating a regular helping of fresh fruits, vegetables and whole grains, reduces the incidence of cancers. Dogs are omnivores, unlike cats which are carnivores. Therefore, a properly formulated diet, which not only contains all the right nutrients in the correct proportions, but also includes added vitamins, minerals and anti-oxidants which help fight off carcinogens, can prevent cancer and help your pet live a happy healthy life.
So what do you do if you have taken all the known preventative measures and your animal still develops cancer? There are approximately 200 different types of cancer and the starting point will be to identify exactly what type of cancer your animal has and what stage that cancer is at. In nature, animals cannot afford to show symptoms of disease at an early stage because “the law of the jungle” determines that weaker animals will be “taken out” by stronger ones in the pack or by predators. This natural instinct also holds true for our domestic animals and therefore the initial symptoms of disease may go unnoticed until the disease has progressed so far that the signs can no longer be hidden. By such time the disease is usually far progressed and the prognosis becomes worse with every passing day. It is therefore absolutely vital that you have your animal checked out by the veterinarian as soon as you suspect something is wrong. Your observations and “gut-feel” about their animal is often the reason why the vet can make the diagnosis at an early stage and provide suitable treatment with a much better prognostic outcome.
External cancers which are the tumours or growth type can usually be seen with the naked eye and be attended to as soon as observed. Internal cancers which grow in organs may not be visible nor might their effects be visible until the majority of the organ is affected. It is therefore of paramount importance that your animal visits the vet at least once a year for a regular check-up and wellness examination during which the animal may also be vaccinated if needed. During this examination the vet should examine all the external structures of the body like the ears, eyes, nose and mouth, the skin and the superficial glands lying below the surface of the skin, as well as the internal organs by listening to the heart and lungs, and doing an abdominal palpation (using the hands to feel and touch the organs inside the abdomen). In certain cases a rectal exam may be needed, or certain routine laboratory tests may be performed like analysis of the urine or a stool sample examination. Many cancers have been picked up by vets during these routine yearly examinations and have been treated successfully before they blow up into full clinical disease which can either not be treated or treated at great expense with a guarded prognosis. Not all internal cancers can be picked up during the annual wellness examination and therefore the owner’s observation of their animal’s health and well-being makes up an important part of the vet’s awareness to examine for signs of cancer.
Once the presence and type of a cancer has been confirmed and it has been staged (indicating the progression of the cancer), the vet will suggest treatment. In cases where the cancer is very far advanced, has spread to other organs, or where the prognosis even with extensive and expensive treatment may be poor, the vet may suggest euthanasia.
In cases where the prognosis is good several types of treatment may be suggested depending on the type and stage of cancer.
Surgery still remains one of the most successful treatments for cancer. This may range from minor surgery like the removal of a small tumour under local anaesthetic to major and extensive surgery like the removal of an organ or body part. In many types of cancer surgical treatment will be combined with other modalities from radiation therapy (to “shrink” a tumour before surgery) to chemotherapy after surgery (to prevent further spread).
Even though most practices have diagnostic X-ray machines which may theoretically be used for radiation therapy, it is not a service which is available in most veterinary practices and will require you to take your animal to a specialist facility. The most common form of radiation therapy is external beam radiotherapy. Your animal will sit or lie on a couch or surface where an external source of radiation is pointed at the particular part of the body which is affected. As most animals do not sit still for extended periods of time your animal will most likely be sedated). Kilo voltage (“superficial”) X-rays are used for treating skin cancer and superficial structures. Mega voltage (“deep”) X-rays are used to treat deep-seated tumours (e.g. bladder, bowel, prostate, lung, or brain). Superficial X-rays can be provided through the same machines used for diagnostic purposes and the deep X-rays are provided by linear accelerators or the older type Cobalt units.
Chemotherapy refers to the use of chemical compounds or drugs to fight and kill cancer cells. Unfortunately it is very difficult for these drugs to target cancer cells only and therefore normal healthy cells of the body may also be affected, leading to significant side effects.
Chemotherapeutic drugs are available in injectable as well as tablet form. Commonly when cancer is treated with chemotherapy, a combination of both is used. The drugs given intravenously are usually injected with the aid of a drip line. As these drugs tend to be very cytotoxic (toxic to cells) they can cause significant damage to healthy tissue if not administered with great care. Therefore your animal will likely be admitted to the veterinary hospital as an in-patient for this procedure. Chemotherapy medications which are administered per mouth may require you to handle the medication with latex gloves to prevent uptake of the medication through your own skin.
Immunotherapy is where immunostimulants (drugs which boost your animals internal defence systems) are administered in certain types of cancer to stimulate the immune system to reject and destroy certain types of cancer.
Photodynamic therapy (PDT) is a form of phototherapy (exposure to specific wavelengths of light using specialised light sources) which use nontoxic light-sensitive compounds that, upon exposure to this light become toxic to targeted malignant and other diseased cells.
Complementary and alternative cancer treatments are a diverse group of health care systems, practices, and products that are not part of conventional medicine. “Complementary medicine” refers to methods and substances used along with conventional medicine, while “alternative medicine” refers to compounds used instead of conventional medicine. Most complementary and alternative medicines for cancer have not been rigorously studied or tested. Some alternative treatments have been investigated and shown to be ineffective but still continue to be marketed and promoted. It is considered to be a specialised discipline and as such may not be something you should expose your animal to unless done through a veterinarian specialising in this field.
Cancer CAN be beaten. As long as your vet has the opportunity to diagnose cancer early and treat it appropriately, your animal has the chance of living a long and healthy life.
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