Equine lymphoma: a review

Lymphoma is the most commonly occurring equine haemopoietic neoplasm, accounting for 1.3–2.8% of all neoplasia identified in horses. The disease broadly takes one of five forms: multicentric, alimentary, cutaneous, mediastinal and solitary extranodal tumours. Lymphoma can be classified by immunophenotype, allowing more accurate prognostication and individualised chemotherapeutic protocols. Clinical signs are usually insidious in onset and clinicopathological changes tend to be broad and non-specific, impeding early antemortem diagnosis. It is not uncommon with internal tumours that a diagnosis is not made until post-mortem examination. Treatment options are limited and often cost-prohibitive, and advanced disease progression at time of diagnosis means that euthanasia is usually opted for, as treatment is very rarely curative. Earlier diagnosis may improve prognosis if therapeutic options are viable to owners, so lymphoma should be considered as a differential diagnosis in many cases.