(excerpts from Equine Disease Quarterly Newsletter – Dr. Alan Loynachan Univ of KY Lexington, KY)

Lymphocytes are White Blood Cells (WBC) and play an important role in the immune system of humans and animals. As like any other cell in the body, the lymphocyte has the potential to become neoplastic (cancerous) resulting in uncontrolled regulation and growth of the cell line. The proliferation of neoplastic lymphocytes is called lymphosarcoma (LSA). Though lymphosarcoma in horses is common, the exact incidence is unknown. Though lymphosarcoma can occur in any age bracket of the horse, the majority of cases seem to occur in horses between the ages of 4-15 years old. The research studies do not implicated any particular breed or gender. Though the cause for LSA is not known, certain bacteria and viruses have been implicated in its development.


There are 4 anatomical categories used for identification of LSA

  • Multicentric (generalized)
  • Cutaneous (skin)
  • Thymic (within the chest cavity)
  • Alimentary (intestinal)


The signs may develop quickly or over several months and the symptoms may be related to organ dysfunction directly, physical obstruction caused by the neoplastic masses, or from neoplastic by-products. Though signs of LSA can vary, common symptoms include: weight loss, depression, subcutaneous edema, fever, anemia, and lymphadenopathy (swollen Lymph nodes). Multicentric, thymic, and cutaneous forms can compress the airways and esophagus and result in respiratory or swallowing abnormalities. The intestinal form can result in colic, diarrhea, and weight loss. Cutaneous nodules may be observed under or within the layers of the skin. The nodule size may vary in size (wax and wane) based on hormonal influence. LSA can create paraneoplastic syndromes including hypercalcemia, pseudohyperparathyroidism, pruritus and alopecia (including itching and hair loss)


Diagnosis is made by the veterinarian locating the intestinal masses by rectal palpation or ultrasound and biopsy of the cutaneous nodules. Definitive diagnosis is made by fine needle aspirates of tumor fluid, surgical biopsies or necropsy samples.


Most horses that are diagnosed with Lymphosarcoma either die or are humanely euthanized within months of developing clinical signs. Horses diagnosed with the cutaneous form typically have a longer survival rate than those horses diagnosed with any of the other three forms of LSA. Treatment is infrequently attempted, but temporary relief may occur with surgical excision of tumors and nodules or with treatment using hormones, chemotherapeutics, immunomodulators, and corticosteroids.


The University of Kentucky Veterinary Diagnostic Laboratory diagnosed 57 cases of equine LSA from September 2009. Diagnoses were made from biopsies, necropsies and cytology. These cases represented 51 horses of 7 different breeds. The age affected ranged from a fetus of 300 days gestational age to 27 year old gelding.

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