Liver Tumors in Cats and Dogs

CE Email comments/questions to [email protected], fax 800-556-3288, or log on to www.VetLearn.com Tumors affecting the liver can be either primary or metastatic. Metastatic involvement is more common than primary hepatobiliary tumors.The four categories of primary hepatic tumors in cats and dogs are hepatocellular, bile duct, mesenchymal, and neuroendocrine. In dogs, malignant variants of these tumors are more common, whereas benign neoplasia, particularly cystic bile duct adenoma, is more frequent in cats. Primary hepatic tumors are morphologically classified as massive, nodular, or diffuse.The prognosis is better for massive tumors than for nodular, diffuse, or metastatic liver tumors because surgical resection is possible and can be curative, particularly for hepatocellular carcinoma in dogs and bile duct adenoma and myelolipoma in cats. In contrast, treatment options are limited for cats and dogs with nodular, diffuse, and metastatic liver tumors as surgery is often not possible and other forms of therapy have not been investigated. multifocal and involve several liver lobes; and diffuse involvement may represent the final spectrum of neoplastic disease with multifocal or coalescing nodules in all liver lobes or diffuse effacement of the hepatic parenchyma. The prognosis for cats and dogs with liver tumors is determined by histology and morphology. The prognosis is good for massive hepatocellular carcinoma (HCC) and for benign tumors because complete surgical resection is possible and their biologic behavior is relatively nonaggressive. In contrast, the prognosis is poor for cats with any type of malignant tumor and for dogs with malignant tumors other than massive HCC. DIAGNOSIS Presenting Signs and Physical Examination Hepatobiliary tumors are symptomatic in approximately 50% of cats and 75% of dogs, especially in animals with malignant tumors. The most common presenting signs are nonspecific and include inappetence, weight loss, lethargy, vomiting, polydipsia/polyuria, and COMPENDIUM 50 January 2004 January 2004 COMPENDIUM Liver Tumors in Cats and Dogs 51 CE hepatic hemangiosarcoma (HSA). Prolonged coagulation times and clotting factor abnormalities have been identified in dogs with hepatobiliary tumors, although these are rarely clinically relevant. Liver enzymes are commonly elevated in dogs with hepatobiliary tumors (Table 2). There is no apparent correlation between the degree of hepatic involvement and the magnitude of liver enzyme alterations; however, liver enzyme abnormalities may provide an indication of the type of tumor and may distinguish primary from metastatic liver tumors. Alkaline phosphatase (ALP) and alanine transferase (ALT) are commonly increased in dogs with primary hepatic tumors. In contrast, aspartate aminotransferase (AST) and bilirubin are more consistently elevated in dogs with metastatic liver tumors. Furthermore, an AST:ALT ratio less than 1 is consistent with HCC or bile duct carcinoma, whereas a neuroendocrine tumor or sarcoma is more likely when the ratio is greater than 1. In general, however, liver enzyme elevations are not specific for the diagnosis of hepatobiliary diseases. Other changes in serum biochemical profile in dogs with hepatic tumors include hypoglycemia, hypoalbuminemia, hyperglobulinemia, and increased preprandial and postprandial bile acids. In contrast to what occurs in dogs, azotemia is often present in cats with hepatobiliary tumors and may be the only biochemical abnormality, although liver enzyme abnormalities, especially in ALT, AST, and total bilirubin, are also common and are significantly higher in cats with malignant tumors. Table 1. Frequency of Morphologic Classifications of Malignant Primary Liver Tumors in Dogs Tumor Type Massive Nodular Diffuse Hepatocellular carcinoma 53%–84% 16%–25% 0%–19% Bile duct carcinoma 37%–46% 0%–46% 17%–54% Neuroendocrine tumor 0% 33% 67% Sarcoma 36% 64% 0% ascites. Seizures, which are uncommon, may be caused by hepatic encephalopathy, paraneoplastic hypoglycemia, or central nervous system metastasis. Icterus is more commonly seen in dogs with extrahepatic bile duct carcinomas or diffuse neuroendocrine tumors. However, these signs rarely assist in differentiating primary and metastatic liver tumors from nonneoplastic hepatic disease. Physical examination findings can be equally unrewarding. A cranial abdominal mass is palpable in up to 75% of cats and dogs with liver tumors, although palpation can be misleading since hepatic enlargement may either be absent in nodular and diffuse forms of liver tumors or missed due to the protected position of the liver in the cranial abdomen deep to the caudal rib cage. Laboratory Tests Hematologic and serum biochemical abnormalities are usually nonspecific. Leukocytosis, anemia, and thrombocytosis are common in dogs with liver tumors. Leukocytosis is probably caused by inflammation and necrosis associated with large liver masses. Anemia is usually mild and nonregenerative. The cause of anemia is unknown, although hypotheses include the presence of chronic disease, inflammation, red blood cell sequestration, and iron deficiency. Thrombocytosis, defined as a platelet count greater than 500 × 10/μl, is seen in approximately 50% of dogs with massive HCC. Proposed causes of thrombocytosis include anemia, iron deficiency, inflammatory cytokines, and paraneoplastic production of thrombopoietin. Anemia and thrombocytopenia can be seen in dogs with primary and metastatic Table 2. Frequency of Hematologic and Serum Biochemical Abnormalities in Cats and Dogs with Hepatobiliary Tumors