Cancer and the Inheritance Factor

Cancer: The word strikes fear in the heart of any dog owner.

By | Posted: Fri Jul 2 00:00:00 PDT 2004

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A very small percentage of human cancers have been linked to heritable causes. About 5 percent of human breast cancer is caused by specific genes, and another 15 percent is thought to be familial. About 15 percent of all colorectal cancers are thought to be hereditary. Some less commonly inherited cancers are retinoblastoma, endocrine tumors, and certain skin cancers. Familial cancers include about 5 percent of ovarian cancers, and 2 percent of endometrial cancer. Lung cancer, melanoma, and prostate cancer also have familial components.  That's in humans. In dogs, there's far less data. A hereditary form of kidney cancer called multifocal renal cystadenocarcinoma and nodular dermatofibrosis (RCND) has been identified in a family of German Shepherd Dogs. It's inherited as an autosomal dominant with high penetrance, but late onset; the gene responsible appears to be on chromosome 5.

More often, certain types of cancer seem to run in breeds. In a survey of cancer rates in various breeds, the Boxer was found to be 35 times more likely to develop cancer than the least likely breed, the Dunker [Norwegian Hound]. Other breeds are more susceptible to specific forms of cancer: Histiocytosis is found much more commonly in Bernese Mountain Dogs, for example. Two cancers of the white blood cells, lymphoma and leukemia, seem overrepresented in Golden Retrievers and Boxers. Melanoma is seen more often in Irish Setters, Gordon Setters, Standard Schnauzers, Miniature Schnauzers, Doberman Pinschers, and Scottish Terriers. Hemangiosarcoma is overrepresented in German Shepherd Dogs, Golden Retrievers, Great Danes, Boxers, English Setters, and several other breeds.

Some cancers that occur more often in certain breeds may be influenced by other physical factors that put the breed at risk. For example, osteosarcoma (bone cancer) is more common in large and giant breeds; this may be related to the greater cell growth necessary in the growth plates of long-legged dogs, rather than "cancer genes." Similarly, squamous cell carcinomas are more common in certain white breeds of dogs, but lightly pigmented or thinly coated dogs in general (especially those exposed to a lot of sunlight) are more susceptible to this form of skin cancer.

Some canine tumors, such as oral papillomas and tranmissable venereal tumors, are spread from dog to dog. Lymphoma in humans (and in some other species) can be caused by a virus. Researchers have not found evidence of that or any other virus causing lymphoma in dogs, however.

So what do you do if cancer strikes? From a breeding viewpoint, you find out what kind of cancer it is, if related dogs have had the same type, and if that cancer is more common in your breed. If there is evidence that it may run in the family, then you must make future breeding decisions involving that family with care, to select mates that do not share the same background.

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