Veterinary
Oncology

Equine lymphoma: a review

02 September 2021
Clinical
15 mins read
02 September 2021
Volume 5 · Issue 5
Figure 1. A horse with ventral oedema of the abdomen.
Figure 1. A horse with ventral oedema of the abdomen.

Abstract

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.

The term lymphoma describes neoplasia of lymphocytic tissue and is used interchangeably with lymphosarcoma and malignant lymphoma. Generally, the term refers to solid tumours without bone marrow involvement, although metastatic spread can lead to subsequent marrow involvement. Lymphoma has been reported to account for 1.3–2.8% of all tumours diagnosed in horses, although one study of 964 equine neoplastic histology submissions found the incidence of lymphoma as high as 14% (Savage, 1998; Schneider, 2003; Knowles et al, 2015). It is also the most commonly occurring equine haemopoietic neoplasm (Muñoz et al, 2009).

The diverse nature of lymphoma and the number of organs potentially affected results in a broad range of non-specific clinical signs and clinicopathological changes, making antemortem diagnosis challenging. While equine oncology is not as developed as that in other species, there are both palliative and curative treatment options available in certain cases. Generally, there is a paucity of data on the use of chemotherapeutics in equine lymphoma cases, with data limited to single case reports or small case series. This review describes the classification of the various forms of lymphoma, diagnostic methods and explores potential treatment options and chemotherapeutic protocols.

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lymphoma
horse
neoplasia
clinicopathology
lymphosarcoma
oncology