Primary hepatic tumors are uncommon in horses and ruminants. They include hepatocellular carcinoma, cholangiocarcinoma, and, rarely, lymphoma, hepatoblastoma (in foals, young horses, alpaca crias), and mixed hamartoma. Cholangiocarcinoma is the most common and is found primarily in middle-aged or older horses. Hepatic carcinomas arise from hepatocytes, bile ducts, or metastasis. Hepatocellular carcinomas generally are found in yearlings to young adult horses and have also been reported in llamas and goats. Adenomas or adenocarcinomas of the liver have been reported in cattle. Hepatic fibrosarcoma and bile duct carcinoma with metastasis to the lungs have been reported in goats. Erythrocytosis, large areas of extramedullary hematopoiesis, and metastasis to the thoracic cavity have been reported in horses with hepatoblastoma. Metastatic melanoma, mesothelioma, and gastric, renal, or mammary carcinoma may result in secondary liver involvement.
Lymphosarcoma is the most common neoplasia of the hematopoietic system in horses. As many as 37% of horses with lymphosarcoma have neoplastic involvement of the spleen, and 41% have neoplastic involvement of the liver. Metastasis of lymphosarcoma of the liver has been reported in cattle, llamas, alpacas, and goats.
The predominant clinical signs with hepatic carcinoma are lethargy and weight loss. A progressively enlarging abdomen, erythrocytosis, persistent hypoglycemia, icterus, and hepatic failure may also occur. Cholangiocarcinoma causes pronounced weight loss before the onset of hepatic failure. Liver hepatocellular and biliary enzyme concentrations may be increased with hepatic carcinoma or cholangiocarcinoma. Gamma-glutamyl transferase (GGT) activity in affected horses is usually very high. Hepatocellular carcinomas are characteristically uniform in appearance on ultrasonographic examination.
Clinical signs of lymphosarcoma in horses vary. Early in the disease, nonspecific signs such as weight loss, anorexia, and lethargy are evident. Lymphosarcoma occasionally may diffusely infiltrate the liver and produce clinical signs of hepatic failure, jaundice, and severe depression. Laboratory findings include hypoglycemia, mild to moderate increases in plasma liver enzymes, hyperbilirubinemia, and abnormally low concentrations of IgM. Ultrasonographic examination helps to detect splenic and hepatic neoplasia. In ruminants, clinical signs produced by tumor growth in other organs (lymph nodes, abomasum, heart, uterus, spinal cord) are often predominant.
The presence and character of the hepatic neoplasia can be confirmed by liver biopsy and microscopic examination of the tissue. Atypical lymphocytes or lymphoblasts may be observed in exfoliative cytology of peritoneal fluid and peripheral blood of some affected animals. Increased serum alpha-fetoprotein concentration may be detected in cases of hepatoblastoma or hepatocellular carcinoma.
