Arm Your Dog Against The Effects Of Aging
Unfortunately, cancer is a common canine ailment. It is a killer in dogs, just as it is in humans. In a 1997 Swedish study involving 222,000 dogs, the proportional mortality rate for cancer was 18.6 percent of the recorded deaths in 1993.1 These high-risk breeds (more than 10 percent dying of cancer) are: Boxer (36.9 percent), Giant Schnauzer (36.9 percent), Bernese Mountain Dog (32.7 percent), Irish Wolfhound (24.8 percent), Cocker Spaniel (22.2 percent), Doberman Pinscher (22.2 percent), Pomeranian (19.0 percent), Newfoundland (16.8 percent), German Shepherd Dog (14.8 percent), Saint Bernard (13.1 percent), Great Dane (12.3 percent), Greyhound (12.3 percent) and Basset Hound (percentage unknown, but the breed does have a genetic predisposition to lymphomas).
Skin. The most prevalent tumor location in dogs is the skin, and 20 percent to 30 percent of these are malignant. They can be composed of mast cells (which contain substances released when an allergic reaction occurs), histiocytes (which share the physical characteristics of macrophages), squamous cells (which make up most of the cells in the skin's outer layer) and melanin-pigmented cells.
Schnauzers, Beagles, Labrador Retrievers, Boston Terriers and mixed-breeds are predisposed to mast cell tumors, and Bull Terriers, Boxers, Dachshunds, Cocker Spaniels, Great Danes and Shetland Sheepdogs are most prone to histiocytomas (tumors containing histiocytes). Histiocytomas most often are benign and commonly will occur before 2 years of age.
Lightly pigmented dogs such as Dalmatians, Beagles, Whippets and white English Bull Terriers are at the highest risk for squamous cell carcinoma, because exposure to sunlight may induce these malignancies. Nail bed squamous cell carcinomas are most prevalent in large breed dogs with black coats. Melanomas, tumors composed of melanin-pigmented cells, comprise 5 percent to 7 percent of skin tumors and usually are malignant if found within the mouth and nail beds.
Other tumors. Although skin tumors are most common, tumors do appear elsewhere. More than any other domestic species, brain tumors are most often seen in dogs.2,3 One of the most common (7 percent to 24 percent, depending on the breed) tumor types found in dogs is lymphoma. Genetic predisposition has been documented in a line of Bullmastiffs, Otterhounds, Rottweilers and Scottish Terriers. Other breeds thought to be predisposed are Boxers, Basset Hounds, Saint Bernards, Airedale Terriers and English Bulldogs.
Osteosarcoma is the most common primary bone tumor of dogs. Size rather than breed is considered more of a risk factor, and this tumor type most often is seen in the large and giant breeds. A genetic predisposition may be seen in Saint Bernards, Great Danes, Irish Setters, Doberman Pinchers, German Shepherd Dogs and Golden Retrievers.
The gender of the dog comes into play, too. The most common tumor (41 percent to 53 percent, depending on the breed) of female dogs is the mammary gland tumor. Incidence can be reduced by as much as 25 percent if the dog is spayed before her first heat cycle. Poodles, English Springer Spaniels, Brittanys, English Setters, Pointers, Fox Terriers, Boston Terriers and Cocker Spaniels are most prone to these tumors.
Testicular tumors are the second most common tumor type of the intact male dog. Males with undescended testicles are 13.6 times more likely to develop this form of cancer. Perianal tumors are the third most common tumor in maledogs. These most often are benign and are thought to be linked to testosterone. Samoyeds, Cocker Spaniels, Beagles and English Bulldogs seem to have a higher incidence.
Although some tumors may not affect a large percentage of canines, they are cause for concern nonetheless. Six percent of all dog tumors are oral and usually are malignant. Intranasal tumors comprise 1 percent of all dog tumors and usually are malignant. Long-nosed dogs may be predisposed to this condition.
Can you safeguard your canine from these tumors? Cancer prevention is not well understood. In its simplest sense, cancer is a failure of the immune system to check uncontrolled growth of certain cells. As these cells multiply unchecked, they form tumors. If the tumors are unchecked, they metastasize, that is, they send out cancer cells that multiply into tumors in other parts of the body. The various initiating factors that cause the initial cell growth are hot topics in cancer research, but they still are poorly understood. One predisposing factor, however, is well documented-age.
Costs of treatment and poor prognoses often mean dogs that develop cancer are euthanized. Fortunately, treatment options are becoming more available as different therapeutic modalities used in human cancer patients augment veterinary clinical practice. Surgical excision generally is best, but the tumor type and location dictate the therapy chosen. Radiation treatments and new chemotherapy drugs now are available to clinicians. Several universities, including the University of Colorado, have become canine cancer centers. Newer treatment strategies now being investigated include gene therapy, drugs that inhibit the metastasis process and chemotherapy-impregnated implants that release drugs in a slow, steady manner.4