Cancer in dogs is common: one in four dogs will develop dog
tumours at some point in their life. Cancer in dogs kills half of all dogs older than ten. Dog
tumours are, with the exception of accidents, the number one cause of death in domesticated dogs.
Like humans, cancer in dogs can strike any organ in the body. Dog
tumours may not produce symptoms or discomfort until the tumour has grown to a considerable size and the cancer is well-advanced.
Skin Cancer in Dogs
Skin cancer is the most common cancer in dogs, especially older animals. Skin cancer in dogs may develop as a lump, abnormal mole or lesion on the dog's skin.
Light-coated dogs seem more susceptible to skin cancer than other dogs, especially if they spend significant amounts of time outdoors. Often skin cancer in dogs can be cured by surgical removal of the dog
Breast Cancer and Dog Tumours
Breast cancer in dogs occurs most often in intact females: fifty percent of unspayed females develop breast cancer. Purebred dogs have twice the risk of developing breast cancer as mixed breeds, possibly because fewer purebred dogs are spayed.
Most cases of breast cancer in dogs (approximately 76 percent) are adenocarcinomas, or
tumours that develop in the dog's breast duct cell linings.
Risks factors associated with breast cancer in dogs include obesity, dietary factors and being underweight. Obesity is an especially serious risk factor: breast tumors in obese dogs are four times more likely to be malignant and spread aggressively than breast cancer in dogs of healthy weight.
Testicular Cancer in Dogs
In humans, one type of testicular cancer predominates: the seminomas. Testicular cancer in dogs can be caused by three different dog
tumours: seminomas, interstitial cell tumours and Sertoli cell
Dogs with an undescended testicle (cryptorchidism) or inguinal hernia have a higher than normal risk of developing testicular cancer. Neutering a dog removes the testicles and therefore eliminates the risk of testicular cancer.
Dog Tumours Affecting Bones
Bone cancer in dogs, or osteosarcoma, is an aggressive cancer that often spreads to the lungs. Large dogs are to be more at risk of developing bone
tumours than average dogs: up to sixty times more likely if the dog weighs more than eighty pounds.
Leg bones are most likely to develop osteosarcoma, and some research indicates that taller dogs have an increased risk of bone
tumours. Unlike testicular and breast cancer, spaying or neutering actually increases the risk of bone cancer in dogs twofold, possibly because sterilization alters hormone levels.
Other Dog Tumours
Cancer in dogs may also affect the nose, bladder, prostate and immune system. Prostate cancer in dogs is much more aggressive in humans and spreads rapidly.
Certain cancers are rarely seen in dogs. For example dog tumours rarely develop in the colon, rectum, lungs, ovaries or uterus. When lung cancer in dogs does develop, the dog has often been exposed to long-term
second-hand cigarette smoke.
Symptoms of Cancer in Dogs
Cancer in dogs produces many different symptoms, depending on the nature of the dog
tumour. Often initial symptoms of dog tumours are mistaken for flu-like symptoms, being "under the weather" or simply "getting old." A sudden change in appetite, weight or temperament should be reason enough to schedule a veterinary visit, as any of these changes could result from dog
General symptoms that may indicate cancer in dogs include:
bleeding or discharge from the mouth, nose or ears
blood in stool or urine
change in appetite
chronic sores or lesions
difficulty swallowing or eating
difficulty voiding bowels or bladder
loss of energy
rectal bleeding or discharge
Diagnosing Dog Tumours: Biopsy and Surgery
Diagnosis of cancer in dogs usually begins with a physical exam and x-rays. Exploratory surgery may reveal dog
tumours that x-rays miss. When a tumour is detected a biopsy must be performed. This may occur before surgery, if a small sample of dog
tumour is collected. A biopsy may also occur after cancer surgery, if dog
tumours are small and do not show signs of spreading.
Treating Cancer in Dogs
Once a biopsy confirms the presence of cancer in dogs, a number of treatment options are available. Surgery can be used to cure many skin cancers, and in some cases is an option for internal dog
Chemotherapy may be used instead of surgery, or in combination with surgical procedures. Chemotherapy uses systemic medications that kill all fast-growing cells in the dog's body, including cells in dog
As chemotherapy affects the dog's entire body, it can cause unpleasant side effects, including hair loss, nausea and vomiting. Side effects of chemotherapy must be balanced against the benefits of the drugs when fighting cancer in dogs.