If your horse is diagnosed with lymphoma—an uncommon type of equine cancer that originates in the lymphatic system—you’ll likely want to know how effective treatment is before pursuing it. After all, chemotherapy is expensive. But veterinarians haven’t had concrete information, as there have been no studies on long-term outcomes after chemotherapy for horses with lymphoma.

To fill that gap, Daniela Luethy, DVM, Dipl. ACVIM, a large animal internal medicine lecturer at the University of Pennsylvania School of Veterinary Medicine New Bolton Center, in Kennett Square, and colleagues recently conducted a retrospective study on the topic.

Clinical signs of cancer in horses can be vague, nonspecific (such as weight loss, failure to gain weight, or fever), and unapparent until the disease is in an advanced state, making it challenging to diagnose. Lymphoma is a type of hematologic (blood) cancer in which the tumor cells arise from lymphocytes, a type of white blood cell. Multicentric lymphoma can, essentially, affect the entire body, whereas cutaneous lymphoma affects the skin.

The team reviewed the medical records of horses treated with systemic chemotherapy—in which medications travel through the horse’s bloodstream to reach multiple parts of the body