Cancer is one of the most common diseases found in dogs and is comparable with cancer rates in humans. Age plays a significant part as the risks of contracting the disease, increase as the dog gets older. Cancer occurs when cell growth mutates both on and inside the body. Cell growth is normally controlled by the DNA code in every cell. In a tumourous cell an error has occurred causing abnormal growth. If the error is minor it is called benign and if major growth happens it is called malignant. Tumours that form from glandular cells are called carcinomas and ones that arise from skin, muscle, bone and fibrous tissues are called sarcomas. The original site of the tumour is called the primary cancer but sometimes cancerous cells break off and move around the body to lodge elsewhere, (as in the lungs, liver, bone marrow, and kidneys) and are called metastatic tumours. The exact cause is unknown but there are a variety of factors that point to being possible causes. Some cancers, such as breast, ovarian and testicular cancer can be prevented by spaying or neutering the dog. Common types of cancer are skin, breast, testicular, lymphomas and abdominal cancers.
Diagnoses.
Cancers can be diagnosed by a veterinary surgeon through blood tests, x rays, and biopsy’s. A biopsy is a procedure whereby snippets of tumour tissue are surgically extracted and examined to determine the possibility of a tumour and as to whether it is malignant or benign. Benign tumours are commonly seen as lipomas, (fatty tissue) or papillomas, (cauliflower like growths that form within the skin layers.)
Symptoms.
Symptoms can be varied and the tumour may be in an advanced stage before a diagnoses is made. Signs to look out for are:
• Loss of appetite.
• Weight loss.
• Swellings, sores or skin blemishes that do not heal.
• Abnormal growths or suspicious lumps.
• Swellings in the mouth and around the teeth when the teeth themselves seem healthy.
• Tiredness and lethargy.
• Poor mobility.
• Difficulty in eating or swallowing.
• Any breathing difficulties accompanied by coughing, wheezing, or sneezing.
• Inability to urinate or blood in the urine.
• Difficulty in passing stools or blood in the stools.
• Excessive thirst and an increase in urinating.
• Abdominal enlargement causing a pot bellied appearance.
Of course, mostly these symptoms may just be the results of a virus or an infection or even the dog just being a bit off colour but it is vitally important that the animal is seen by the vet to rule out anything untoward.
Risk Factors.
1) Humans are increasingly aware of environmental pollution and the effects on the human body. Dog owners should be aware that their pets face the same risks. Spaying and neutering a dog does negate the risks of mammary cancer and testicular cancer. In fact spaying a female before the first heat cycle means half the risk again of those spayed later on.
2) Dogs that receive excessive exposure to strong sunlight are at risk from skin cancers, especially dogs that have little or no hair, or no pigmentation. Often skin cancer is found on the underbelly or the inside areas of the legs. Dogs at risk include Pointers, Bull Terriers, and Dalmatians. In Dalmatians the cancer will form around a black spotted area but never enters the black skin. Skin cancers make up over half of the total number of cancers in dogs. Most common are Papillomas which are benign, cause no damage and can be surgically removed. Problems may occur if the area removed leaves little skin to cover the site of the tumour. The next most common skin cancers are called Mastocytomas, (mast cell tumours.) They are locally invasive, malignant, but do not migrate to other sites. Another risk factor for skin cancer is contact with carcinogens as found in the dog’s environment.
3) Dogs have a higher incidence of nasal sinus cancers due to sniffing the ground and to the length of their noses. Carcinogens, (an agent that is likely to cause cancer) from herbicides and pesticides are the main culprits in rural areas. Pollution from cars and industry may also cause nasal cancers.
4) The fourth most common site for cancer in dogs is cancer of the mouth. Carcinogens in the air fall onto the dog’s coat and are ingested as the dog grooms itself. The oral tissues are affected and the cancer manifests itself as swellings around a tooth. Breeds susceptible to oral cancer are German Shepherds, Chow’s, Black Cocker Spaniels and Scottish Terriers. Unfortunately these tumours are often bleeding by the time they are noticed and a large percent of them are highly malignant. The dog is usually aged between six to ten years old and as any surgery will drastically affect the animal one must look at the life expectancy before making the decision to operate.
5) Trauma or previous injury sites may develop cancer. Sarcoma’s can develop around sites of previous bone fractures. Dogs that suffer from chronic inflammation run the risk of contracting cancer. Dogs rarely get cancer of the gastro-intestinal tract due to their high fibre diet and the fact that they do not smoke although there is now thought to be a link between passive smoking and cancer in dogs.
6) Another risk factor of the dog getting cancer is genetics. Some breeds are genetically predisposed to tumours. Breeds such as Boxers or the giant breeds such as Great Danes, Wolfhounds and so on are particularly vulnerable to developing cancer. Golden Retrievers have a decreased risk of developing cancer.
7) The dog’s diet may contain cancer causing agents as may their environment. Formaldehyde, Chlorine and Nitrates are oncogenic chemicals that are known to cause cancer. Some agents such as asbestos and radiation cause cancer through chronic irritation and inflammation. Certain viruses have been found to cause cancer in dogs.
In unspayed older dogs mammary gland tumours are common. Usually they develop between six to ten years of age. The hormone Progesterone is responsible. If caught early mammary tumours can be surgically removed and are not usually highly malignant.
9) Osteosarcomas, (bone cancers) occur in giant and the large breeds and form particularly in the long bones of the legs. The symptoms are lameness and weakness. These tumours are highly malignant and often metastasize in the lungs causing coughing and wheezing. Paradoxically, neutered male dogs have a higher risk of Osteosarcomas. Amputation of the limbs is the key to treatment.
10) The immune system and hormones also play a role in causing cancer. Very young or very old dogs often have a decreased immune-response which may lead to an increased susceptibility to cancer when exposed to carcinogens. Hormones are another internal factor that plays a major role in the development of mammary, prostate, and ovarian. Thyroid, testicular and bone cancers. Hormones in a young dog dictate how the cells are signalled to divide to enable growth and organ development. In adult dogs, the hormones manage cell growth and the reproductive cycle. Sometimes hormones are the factor causing tumours. Again, spaying and neutering prevent some of the cancers from forming.
I have lost two of my precious dogs to cancer and sympathise with anyone that has been given the dreaded news that their dog has the big C. There is hope as today we know so much more about the causes and treatments. Feeding a natural diet, plenty of fresh air and exercise are a few of the best things we can do for our dogs. I hope that by sharing my knowledge of the disease, other pet owners will not feel so alone.
Dog Lover.
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