ATo date, there is no evidence that lymphoma in horses is a heritable disease (nor is it known to be in other species). In other species, cats and cows in particular, it can be caused by a virus, but no evidence has been found to support this mechanism of transmission for this disease in the horse.

Lymphoma is a disease of the lymphoid system where some lymphoid cells become neoplastic (tumorous) and grow in an uncontrolled manner. This results in invasion and disruption of the function of a variety of organs, and causes immune suppression in many affected equine patients. There have been many advances in chemotherapy drugs for this disease in the horse, but at best, the medications might only control the disease for a few months or years.

Unfortunately, there is no surefire way to detect the disease earlier than when some problem occurs that can be clinically detected. Leukemia (an increase in the number of white blood cells in body tissues) is a rare feature of lymphoma in the horse, so routine blood work often will not detect it, and there is no specific blood test available. Most often, this disease occurs in a multicentric (having multiple centers of origin), multiorgan situation and the most common clinical sign is weight loss. Colic, fever, ataxia, or respiratory difficulty can also be seen depending on the particular organ(s) affected