Paraneoplastic Signs: First Indicators of Cancer in Horses?

Paraneoplastic Signs: First Indicators of Cancer in Horses?

Paraneoplastic manifestations of cancer are often uncovered during routine blood work, Johnson said.

Photo: Anne M. Eberhardt/The Horse

Hearing that a horse has been diagnosed with cancer is one of many owners' worst nightmares. But is there a way by which veterinarians can discover some cancers' presence earlier, thereby allowing treatment to start sooner? Paraneoplastic manifestations of cancer--problems that are not due to the cancer's physical presence, but to the cancer's hormone secretion--are often the first clue a horse has developed the disease.

Philip J. Johnson, BVSc(Hons), MS, Dipl. ACVIM, Dipl. ECEIM, MRCVS, professor of internal medicine at the University of Missouri's College of Veterinary Medicine, discussed paraneoplastic conditions at the 2011 American Veterinary Medical Association Convention, held July 16-19 in St. Louis, Mo.

"Sometimes the paraneoplastic manifestation is the most important and earliest sign of cancer," he explained. "For example, we often see an older horse that is weak, inappetant, and losing weight as a result of the cancer, but there is no sign of that cancer on physical examination.

"So the veterinarian might run routine blood work and notice an elevated blood calcium concentration. This abnormality, called hypercalcemia, has several possible causes, one of which is a paraneoplastic manifestation of underlying cancer."

Paraneoplastic manifestations of different forms of cancer might include hypercalcemia, hypertrophic osteopathy (which results in painful limb swelling), and paraneoplastic fever. The cancer itself, which secretes chemicals that work like the body's natural hormones, causes these side effects. The body responds to the secretion of these hormones by causing problems such as the aforementioned manifestations, Johnson explained.

Johnson noted that the most common equine cancers, such as skin tumors, do not typically provoke paraneoplastic effects; horses that display paraneoplasic manifestations generally are afflicted with an internal cancer, such as thoracic cancer (that occurs within the chest).

Much like cancer itself, there is nothing an owner can do to prevent paraneoplastic manifestations from developing. These manifestations are managed by locating the primary cancer and treating or removing it promptly.

Additionally, veterinarians have found they are able to also use paraneoplastic manifestations to gauge how well a horse responds to cancer treatment.

"Paraneoplastic signs should diminish if the cancer is successfully removed or responds to treatment," Johnson explained.

About the Author

Marie Rosenthal, MS

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