Myelomas are cancers of the B type lymphocytes and rare in horses. They can occur either within the bone marrow (lymphocytic leukemia) or outside of the bones as solitary tumors (plasmacytoma). The bone marrow type is the most common type in horses. Common manifestations include limb edema, ataxia, lameness, nose bleeding, lymph node enlargement, weight loss, and depressed appetite. They occur in horses of all ages. This article discusses the diagnosis, treatment and prognosis of these cancers in horses.

Symptoms are associated with the site of a tumor invasion. Common manifestations include limb edema, ataxia, lameness, nose bleeding, lymph node enlargement, weight loss, and depressed appetite. Secondary bacterial infections are common. The two most common laboratory findings include, anemia and a hyperglobulinemia. A monoclonal gammopathy is detected in nearly all cases. If the disease is widespread through the bone marrow, the anemia may be severe and accompanied by a decreased white blood cell count and low platelets. If the gammopathy is severe, unusual bleeding episodes may occur.