With lymphosarcoma, some lymphoid cells become and grow in an uncontrolled manner. This results in invasion and disruption of the function of a variety of organs and causes immune suppression. The majority of cases occur in horses aged 4 to 15 years, but cases have been described in horses of all ages. There are no proven sex or breed predispositions.
Four anatomical categories are frequently utilized for classification of lymphosarcoma:
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Clinical signs can develop abruptly or over several months. Signs can develop due to organ dysfunction directly related to infiltration by neoplastic lymphocytes; physical obstruction caused by neoplastic masses; or from neoplastic by-products. Depression, weight loss, subcutaneous edema, fever, anemia, and lymphadenopathy (swollen lymph nodes) are the most commonly observed clinical signs, but signs can vary based on the affected organs. Veterinarians might suspect a diagnosis of cancer after visualization of cutaneous nodules, transrectal palpation of abdominal masses, or detection of masses by radiology, ultrasonography, or surgery. Clinical differentiation of neoplasia from non-neoplastic lesions is difficult. A definitive diagnosis of lymphosarcoma is made by microscopic visualization of neoplastic lymphocytes in body fluids, fine needle aspirates, surgical biopsies, or necropsy samples. The majority of horses diagnosed with lymphosarcoma either die or are humanely euthanized within months after developing clinical signs. Horses with the cutaneous form typically have longer survival times in comparison to those with other forms. Treatment is infrequently attempted, but temporary improvement might occur following surgical excision, or treatment with hormones, chemotherapeutics, immunomodulators, and corticosteroids. (an increase in the number of abnormal white blood cells in body tissues) is a rare feature of lymphoma in the horse, so routine blood work often will not detect it, and there is no specific blood test available.
Prognosis is always grave.
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