Clinical signs of cancer in horses can be vague, non-specific (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.
Cancer might be rare in horses compared to humans and small animals, but it occurs and requires treatment nonetheless, often with chemotherapy.
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.
Treatment typically doesn’t cure lymphoma, although veterinarians can use it, in some cases, to slow or reverse clinical sign progression and extend the horse’s lifespan.
At the 2018 American College of Veterinary Internal Medicine Forum, held June 14-16 in Seattle, Washington, Daniela Luethy, DVM, Dipl. ACVIM, a large animal internal medicine lecturer at the University of Pennsylvania School of Veterinary Medicine, in Kennett Square said "Findings show that chemotherapy can be used successfully for treating equine lymphoma. It hasn’t always been clear, however, just how effective chemotherapy is at fighting equine cancer. But recent research suggests that, for equine lymphoma at least, chemotherapy can help horses achieve remission and extend their lifespans for several months or years."
The most common lymphoma immunohistochemical classification (essentially, the type of lymphoma) was T-cell rich large B-cell, found in horses. Further, biopsies from some horses’ tumors tested positive for the gammaherpesvirus equine herpesvirus-5 (EHV-5). Both the T-cell rich large B-cell and equine gamma herpesvirus are the known types of lymphoma cancer.