A tumor is tissue growth composed of abnormal cells that grow in an uncontrolled manner. There are benign tumors and malignant tumors. Benign means the tumor compresses the tissue surrounding it but does not invade. Malignant means the tumor has the ability to invade other tissues via the bloodstream or the lymphatic system and create a second tumor. Cancer usually refers to malignant tumors.
As with people, pets can get cancer in many different organs including bones, liver, kidneys, stomach/intestines, lungs, mouth, brain and lymph nodes. Cancers generally arise by a single cell that has undergone genetic mutations (abnormal changes in the gene) which then affects the genes that control growth and the type of tissue to develop. Causes of these mutations include viruses, chemicals, ultraviolet radiation (prolonged sunlight) or x-rays (prolonged ionizing radiation), hormones and parasites.
Hormones especially play a big role in mammary (breast) cancer in dogs and cats. Mammary cancer in dogs has been proven to be hormone dependent. A dog's risk of mammary tumors decreases with eary spay surgery. If she is spayed prior to her first heat cycle, the risk is 0.05%, after the first heat cycle it is 8%, and then the risk increases to 26%. There has been no evidence that an early pregnancy in the dog will protect her from mammary tumors or cancer. In dogs, 50% of the mammary tumors are found to be malignant. Cats spayed by 6 months of age have a greatly reduced risk of mammary cancer. In cats, 85% of mammary tumors are malignant and are the third most frequently occurring tumor. Many mammary cancers spread to the lymph nodes, lungs, liver, kidneys and adrenal glands. Since there is a high risk of mammary cancer in female dogs and cats due to hormones, it is extremely important to spay them before their first heat cycle, around 6 months of age.
There are many different signs to watch for. Lumps or masses in the skin, bones or joints are important to have examined, especially if they are growing rapidly or are painful. Tumors are generally not detectable until they have reached 1 cubic cm (3/8 inch) in size. Even these small tumors contain over several million cells. Other signs to look for are pain, chronic lameness, fever, a non-healing wound, weight loss, anorexia, weakness, vomiting and/or diarrhea, coughing and difficulty breathing, sudden blindness, seizures, drinking more than normal and/or urinating larger amounts, and blood clotting abnormalities. Sometimes there are not any clinical signs until the cancer is at a very late stage. Always take your pet to your veterinarian if you have any concerns about your pet's health.
Your veterinarian will help address your concerns about your pet. He or she may need to do some blood work; take x-rays; take a needle sample of the lump or do a biopsy. Other diagnostics are ultrasound, endoscopy or a bone marrow biopsy. Treatments for cancer include surgery, radiation therapy, and chemotherapy. Sometimes these treatments may cure the cancer, or put the cancer into remission for a period of time.
Illness and pet loss may cause many emotions. Do not hesitate to call your veterinarian for help, to ask more questions, or just to talk. There are many pet loss support groups as well that you can contact. Here in Madison, you can call the Dane County Humane Society at 608-838-0413 x 113. On the internet, look under www.petloss.com, or www.deltasociety.org.
