A case report of T-cell lymphoma in a horse

Lymphoma is a solid neoplasm of the lymphoid organs (lymph nodes, spleen, etc.). It is the most common neoplasm of the horse’s haematopoietic system, although not common in absolute terms, and has a prevalence ranging from 1% to 3% of all tumours. It is subtyped into four anatomical forms: multicentric, alimentary, mediastinic and cutaneous. Multicentric lymphoma is the most common form and usually involves the lymph nodes and other lymphoid organs, but it can induce metastases to the liver, lungs and kidneys. The clinical signs of lymphoma are associated with the degree of organ involvement and can include aspecific symptoms such as weight loss, depression, lymphadenopathy, intermittent fever, respiratory disturbances and recurrent colic. The diagnosis of equine lymphoma requires a complete clinical examination including rectal palpation, complete blood count (CBC), extended biochemical profile, bone marrow aspirate sampling, serum electrophoresis, liver and spleen echography and finally, fine-needle aspiration (FNA) or surgical biopsy of enlarged lymph nodes or any other eventual masses occurring. Lymphoma can be classified in terms of degree of malignancy as ‘low’ (prevalence of small lymphocytes similar to those appearing in the peripheral blood) or ‘high’ (composed of large lymphoblasts, when the tumour is more aggressive). The most significant classification is based on the lymphoid cell type from which the neoplasm has originated (T- or B-cell type) (Carlson, 1996; Kelley and Mahaffey, 1998; Savage, 1998; McClure, 2000).