Equine lymphoma

Lymphoma, although rare, is the most common haematopoietic neoplasm encountered in horses and can occur at any age, with horses 4–10 years more commonly affected. Lymphoma can be classified into multicentric, alimentary, mediastinal, cutaneous and solitary. Clinical signs are typically nonspecific until the disease has progressed to end-stage at which time clinical signs reflect function of organ(s) involved. Horses with the cutaneous form of lymphoma typically present with multifocal skin lesions and no other clinical signs. Like the nonspecific clinical signs of lymphoma, results of complete blood count (CBC) and serum biochemistries are not often helpful with diagnosis, but lymphoma should be considered if anaemia, hyperfibrinogenaemia, hyperproteinaemia and hypoalbuminaemia are observed without a clear indication of infectious disease. Identification of neoplastic lymphocytes during cytological examination of a body cavity effusion can confirm the presence of lymphoma. Typically, ante mortem confirmation of lymphoma is made through histopathological examination of a biopsy or cytological examination of a fine needle aspirate of a suspected lesion. Observation of compression or destruction of normal tissue architecture by invading neoplastic cells during histological examination is indicative of lymphoma. Additional diagnostics that may improve our knowledge of equine lymphoma include detection of hormone receptors, immunophenotyping, and immunohistochemical analysis for tumour proliferation rates. Prognosis of horses with lymphoma depends on the form of lymphoma and stage at which the horse is presented but death is the common outcome of this disease. Current treatment options are surgical excision, radiation or administration of chemotherapeutic drugs. Treatment of horses with lymphoma can result in palliation and occasional resolution of this disease. Equine oncology is in its infancy, but through further documentation of horses with lymphoma and their response to therapy, a clearer understanding of the disease process and effective treatment of this neoplasm can be developed.