TUMOURS IN DOGS

Non-Cancerous Tumors in Dogs

Non-Cancerous Tumours in Dogs
A hard lump on or under your dog's skin is alarming, but may not be cancer. Many are actually non-cancerous growths such as lipomas, cysts and histiocytomas. While testing is required to verify that these are indeed non-cancerous tumours, the majority of growths that occur on dogs are benign tumours that may not even require removal.

Lipomas (Fatty Tumours)
Lipomas, or fatty tumours, are the most common non-cancerous tumour found in dogs. Lipomas are deposits of fatty tissue under the skin that are separated from surrounding body fat by a fibrous covering.

Fatty tumours are usually round and smooth. Lipomas are not usually painful, but when they become so large that they interfere with a dog's comfort or mobility they should be removed surgically. Fatty tumours are most common in obese female dogs.

Because some fatty tumours are cancerous, a needle biopsy of the growth may be performed. A needle attached to a syringe is inserted into the fatty tumour and some of the contents removed. The contents are spread onto a microscope slide and examined for the presence of cancer cell.

Cysts
Cysts are common non-cancerous tumours that can occur anywhere on or in a dog's body. Sebaceous cysts are benign tumours that can reach an inch in size. Sebaceous cysts are filled with dead skin cells and sebum (oil) that produces the cheesy substance seen when the cyst is ruptured, either surgically or accidentally.

While usually non-cancerous, cysts may require drainage or surgical removal to prevent infection.

Cocker Spaniels are especially prone to sebaceous cysts.

Histiocytomas
Histiocytomas are very red, dome-shaped growths that appear on the ears, face and feet of younger dogs, most often those under age two. The sudden development of histiocytomas can be alarming.

Histiocytomas are often painful to the touch, but not generally associated with cancer. The exact cause of histiocytomas is unknown, but a viral cause is suspected.

Most histiocytomas resolve on their own within three months, but because they can be itchy a topical steroid may be prescribed. If the growth is causing pain or intense scratching that doesn't resolve with topical steroids, surgical removal is warranted.

Histiocytomas are common in Boxers, Dachshunds, Labrador Retrievers and Staffordshire Terriers.

Perianal Gland Tumours
Perianal gland tumours, or perianal adenomas, are most common in un-neutered male dogs. Perianal gland tumours occur in the cells of the oil glands at the base of the tail around the anus.

While most perianal gland tumours are non-cancerous (adenoma), a biopsy may be required to rule out a cancerous form of perianal gland tumour (adenocarcinoma). Perianal gland tumours can cause pain or become infected—their location makes infection quite likely.

Because perianal adenomas are stimulated by the hormone testosterone, most veterinarians will recommend neutering the dog. The tumour(s) may be removed at the time of neutering or at a later date. If the tumours are small, they can often be "frozen" with liquid nitrogen.

Other Non-Cancerous Tumours
A number of other non-cancerous tumours affect dogs. These include:

Warts are generally harmless. Warts can be caused by a papilloma virus or by an irritant. Warts caused by a papilloma virus can be contagious to other dogs and often affect younger dogs. Papilloma usually produces a large number of warts on the face, neck and/or limbs. Once all the warts resolve the dog is considered immune to the virus.
Skin tags are benign growths that stick out from the skin, and which are sometimes described as looking like "bits of chewing gum" stuck to the skin. Skin tags generally occur in older dogs are usually only removed if they become irritated or bleed. A tick is often mistaken for a skin tag, especially if the tick has attached in an area not easily examined by the owner.
A hematoma is a collection of blood under the skin caused by physical trauma. Hematomas usually resolve by themselves. Earflap hematomas occur when a dog vigorously shakes his head in response to ear infections or ear mites. A large earflap hematoma may require drainage.

Non-Cancerous Tumours or Malignant Growths?
While most non-cancerous tumours are safe, there is always the slim possibility that apparently benign tumours will become malignant.

The best course of action is to have a veterinarian examine any growths on your dog's body and decide whether or not a biopsy is necessary. Like many things, when it comes to non-cancerous tumours, being safe is much better than being sorry.

Tumors and Cancer in Dogs

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 tumours.

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 tumours.

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 tumours.

General symptoms that may indicate cancer in dogs include:

abnormal swelling
bleeding or discharge from the mouth, nose or ears
blood in stool or urine
change in appetite
chronic sores or lesions
depression
difficulty breathing
difficulty swallowing or eating
difficulty voiding bowels or bladder
loss of energy
rectal bleeding or discharge
unpleasant odour
weight loss.

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 tumours.

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 tumours.

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.

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