Lost in the Fog: How Common is Equine Cancer?

The grim diagnosis of 2005 champion sprinter Lost in the Fog's inoperable tumors has raised questions about the occurrence of cancer in equines.

"It's not a common problem in horses in general," said Elizabeth Davis, DVM, Dipl. ACVIM, an assistant professor and the head of equine medicine and surgery at Kansas State University. "Horses don't live as long as some other species do, and usually, cancer is a disease of geriatric individuals. Their lifestyle is a little more controlled so that makes it a little less likely."

Forms of cancer found in horses include melanoma, lymphoma, squamous cell carcinoma, granulosa cell tumor, and cancers of the pituitary gland, thyroid gland, gastrointestinal tract, and bone.

Though statistics show more than 80% of gray horses over the age of 15 will develop at least one melanoma in their life, the tumors are usually benign. The most common form of metastasizing tumor is lymphoma. This tumor spreads to various parts of the body, and there are very limited treatment options for this form of cancer, which affects less than 1% of the horse population.

"Unfortunately, the spleen is an organ with a tremendous number of lymphocytes, a type of white blood cell that lives in the spleen, so it is an organ that they are at risk for developing the disease in," Davis said.

Lost in the Fog is not the only champion from last year to have cancer. Knights Templar, the 2005 Canadian champion 2-year-old filly, was euthanized in July after it was discovered that she had lymphoma.

"We do have some chemotherapeutic protocols that are somewhat effective, but usually in veterinary medicine our goal of treatment is to maintain a good quality of life rather than to treat for a cure of the cancer," Davis said. "To clear the cancer completely from the system is difficult."

Because it is rare and horses do not often show symptoms until it is too late, it can be hard to diagnosis cancer in equines at the early stages.

"Most of the time when I diagnose lymphoma in horses, I will have a client that is just completely blown away because they'll say, 'A month ago I went to a horse show, and he performed great,' " Davis said. "There is no chance that horse was normal a month ago, but horses in general are all heart. They do what they know how to do, they do what they think they are supposed to do, and they are a prey species; therefore, it is to their advantage for survival to not let you know that something's wrong."

About the Author

Amanda Duckworth

Amanda Duckworth is an editorial intern for The Blood-Horse.

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