What Is Cancer?
Cancer is uncontrolled growth of cells. The word “tumor” is used interchangeably, but officially tumor simply means swelling. A cancerous growth may be caused by a mutation of the genetic material in just one cell and grow to be a very large life-threatening mass. Almost any tissue or cell type can develop cancer. Cancer can be a fatal disease or a mere nuisance.
Benign Versus Malignant
In speaking of cancers, the terms “benign” and malignant” are often used. A benign cancer is one that is generally not life threatening. It does not usually spread or metastasize to tissues far away in the body. In general, benign tumors grow slowly and have more specialized cells. Even a benign tumor can kill your dog, though, by putting pressure on tissues such as the brain or eroding locally through large blood vessels.
The many varied cells that make up your dog's body all start from basic cell types. As these basic “stem cells” divide and grow, many of them go on to become very specialized. Think of the many different cell types your dog's body has — they all come from one egg cell and one sperm cell! Each cell has a set life span and number of reproductions it can undergo. But these controls can be lost, and that's when cancer moves in.
Malignant cancers tend to grow very quickly and aggressively. They wipe out normal cells, drain exorbitant amounts of nutrients, and interfere with normal vital functions such as breathing. These cancers often spread to other tissues, sometimes even quite far away in the body. For example, mammary tumors tend to spread, or metastasize, to the lungs.
What Causes Cancer?
The causes of cancer are as varied as the cancers themselves. Environmental factors, genetic predispositions, even viruses have all been implicated in the development of certain cancers. Anything that can influence or change the genetic material in cells that regulates their growth and function is capable of causing a cancer. Cells are mutating all the time in your dog's body, but the immune system normally cleans them up right away. Any dog with a lowered or damaged immune system is more vulnerable to cancer.
A recent study determined that exposure to certain pesticides is a factor in the development of bladder cancer in Scottish terriers. This breed probably has a genetic weakness or predisposition, which the pesticides act upon to cause the cancer. Most cancers have similar multiple influencing factors.
In some cases the cancer agent is well established, such as feline leukemia virus for cats or cigarette smoke for lung cancer in people. Even so, there will still be cats with leukemia virus who don't get cancer and people who chain smoke who don't get lung cancer. So for cancer, there seem to be genetic predispositions that are important as well. Certainly, different breeds of dogs have become associated with different cancers. Giant-breed dogs have a much higher risk of osteosarcoma (bone cancer) than the toy breeds. Boxers are on the list for a relatively high incidence of lymphoma, while it is not a common cancer for cocker spaniels.
What Are the Types of Cancer?
Each cancer is based on a certain type of cell from your dog's body. Your dog could develop liver cancer from some of her liver cells or brain tumors from mutated nerve cells. Carcinomas are malignant tumors rising from epithelial cells — skin cells and cells that line or cover different organs. Sarcomas tend to develop out of underlying tissues such as bone, liver, and spleen. Adenomas are cancer of glandular tissues like the thyroid.
As mentioned above, cancers are labeled malignant or benign. Each individual type of cancer acts differently and will have a different prognosis and treatment plan.
