An introduction to equine oncology.

Many people are surprised to hear cancer occurs in horses and that it is a medical condition that is treatable. Horses have been treated for cancer for years, however, their treatment has not evolved at the rate of humans, dogs and cats. Some may even say equine oncology is still in its infancy. The literature on equine oncology is quite small compared to other species. Few large studies exist on the many equine cancer’s out there. The majority of equine oncology literature is case reports for different cancer’s along with chemotherapy dose finding studies.

Equine oncology has lagged behind other species due to a variety of factors such as cost, knowledge and the horses changing position in society. Horses were originally kept for utility and transportation. Over the years their endearing qualities have emerged and they have been keep both for sport as well as beloved family pets. Equine medicine has advanced rapidly over the years allowing us to successfully treat more and more health conditions. Our knowledge of equine oncology originally started with identifying which cancers horses get, and how they were similar or dissimilar to to those of other species. The treatment of these tumors slowly began to mirror other species with surgery, chemotherapy and even radiation therapy being utilized. Giving palliative chemotherapy to horses presented it’s own challenges due to the size of horses and the cost of some drugs. Compared to other species horses can sometimes require very large volumes of chemotherapy to achieve the proper dose needed to treat their cancers.

Horses are noted to acquire many of the same cancers we see in other species. Skin tumors have tended to be the quickest to be recognize in large in part due to the grooming required for most horses and their short smooth coats. The incidence of other tumors is not as well characterized, however, some studies have been able to obtain data from university records as well as abattoirs. The most common tumors in horses are noted to be squamous cell carcinoma, sarcoids, nerve sheath tumors, melanoma and lymphoma. Over the years data on breed prevalence has also emerged, as well as a few studies on the genetic mutations associated with some cancers. These discoveries expand our information on equine cancer and allow us to potentially apply this information to other species.

Should we treat horses for cancer? This is a personal decision made by each owner, one that ideally should be made with as much knowledge as possible and realistic goals. In general if treatment is aimed at relieving discomfort, extending and maintaining quality of life, therapy should be considered. If an improvement in quality of life is simply not possible treatment is not likely worthy. For each case where we make a horse’s life better we all (veterinarians and owners) gain knowledge to help the next horse and advance medicine. Horses are long-lived animals, the time spend with them and the dedication of some horse owners can be tremendous. One could argue that not offering any cancer treatment options to horse owners is a disservice to them.


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