Intestinal Cancer in Horses: Expect the Unexpected

Consider cancer as a possibility in older horses with long-bone fractures and no history of trauma, encouraged a group of veterinarians from Oklahoma State University's Center for Veterinary Health Sciences.

Cancer is relatively rare in horses, and intestinal cancers are even more unusual. Because intestinal adenocarcinomas are especially rare, they are not often considered as an underlying cause of equine fractures.

In the horse, intestinal cancers such as intestinal adenocarcinoma, leiomyoma, leiomyosarcoma, myxosarcoma, ganglioneuroma, nerve sheath tumor, and carcinoid are challenging to differentiate from other conditions such as inflammatory bowel disease and internal abscesses. Nonetheless, a definitive diagnosis is essential for veterinarians to give horse owners appropriate treatment regimens and prognoses.

Unfortunately, early diagnosis of intestinal neoplasia is difficult because clinical signs are often not noted until an advanced stage of disease. Hallmark clinical signs of intestinal neoplasia (tumor), including adenocarcinoma, can include:

  • Weight loss
  • Inappetence
  • Intermittent colic
  • Diarrhea
  • Fever
  • Exercise intolerance
  • Hypoalbuminemia

Signs of intestinal cancers, however, are not always so clear, particularly if the cancer has spread to distant sites (metastasized).

Recently, a group of veterinarians from Oklahoma State University’s Center for Veterinary Health Sciences diagnosed intestinal adenocarcinoma in a 19-year-old Quarter Horse mare with a fractured humerus. A battery of tests led the researchers to a preliminary diagnosis of a poorly differentiated neoplasm, which bode poorly for the mare.

Unfortunately, intestinal adenocarcinoma was not diagnosed until the time of a post mortem examination. The veterinarians did learn from this case and even speculate that this condition "may have been previously overlooked in instances of long-bone fracture in older horses without an obvious traumatic incident."

The study authors stated that this case report highlights "the need for differential diagnosis in these particular circumstances and of which clinicians should be aware of."

The case report, "Occult metastatic intestinal adenocarcinoma resulting in pathological fracture of the proximal humerus," was published in the December 2009 edition of the Equine Veterinary Journal. Background information on intestinal neoplasias in horses is also available in a 2006 article published in the Journal of Internal Veterinary Medicine.

The abstract is available on PubMed.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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