Canine neuroendocrine epithelial tumors

Tumors arising from the neuroendocrine epithelium (carcinoids) account for 13% of primary canine hepatobiliary tumors (Table 2) and have been demonstrated to most frequently involve hepatic parenchyma and to sporadically involve biliary tissue. No breed or sex predilection has been established; however, these neoplasms typically affect younger dogs (average 8 to 9.8 years)—more than two-thirds of the dogs are less than 10 years old.^4,36,37 About 20% of dogs exhibit icterus, and in contrast to other tumor histologic types, hepatomegaly is often not detected on physical examination.^36,37 The clinical signs mimic those of other hepatobiliary tumors; however, ascites are more common.⁴

Hematologic changes may include anemia and leukocytosis. Trends in liver enzyme activities are more consistent for neuroendocrine carcinomas than they are for biliary carcinomas—more than 75% of the affected dogs have elevated ALT and ALP activities, and nearly two-thirds are hyperbilirubinemic (Table 3). Unlike hepatocellular carcinomas and biliary carcinomas, carcinoid tumors are most often diffuse in nature and affect most of the liver parenchyma.^4,36,37 At necropsy, nearly all patients have metastasis, most commonly to the lymph nodes, peritoneum, and lungs.^4,36 Despite the reported metastatic nature and suspected poor prognosis of carcinoid tumors based on necropsy studies alone, early detection may allow better treatment options, such as resection, and, thus, the true prognosis remains undetermined.

Sarcomas account for less than 15% of primary hepatobiliary tumors in dogs (Table 2).⁴ In general, primary hepatic sarcomas occur in older dogs (average 11 years), and females are at an increased risk. The clinical signs are comparable to those of other hepatobiliary diseases, with variable changes in hematologic and biochemical parameters (Table 3).⁴

Figure 2. An ultrasonogram of a 9-year-old male castrated German shepherd presenting for evaluation of episodic weakness and lethargy. A large liver mass is identified, characterized by a mixed echogenic pattern with multiple hypoechoic cavitated lesions. Microscopic examination confirmed the liver tumor to be hemangiosarcoma.

FELINE HEPATOBILIARY TUMORS

Figure 3. The exploratory laparotomy findings from a 7-year-old female spayed domestic shorthaired cat presented for evaluation of subtle weight loss, elevated liver enzyme activities, and icterus. The results of the histologic examination of the resected hepatic mass were consistent with a benign hepatic adenoma.

Clinical signs, if demonstrated by affected cats, are variable and may include anorexia, weight loss, lethargy, intermittent vomiting, and icterus.^39-41 Although complete staging is typically recommended to confirm metastatic disease in cats, interpret additional hepatic lesions with caution, as 16% to 25% of cats with hepatobiliary tumors may have multiple benign lesions throughout the liver (see text titled "Definitively diagnosing hepatobiliary tumors in dogs and cats" at the end of the article).^39,40

Feline biliary adenocarcinomas

Figure 4A. An ultrasonogram of a 12-year-old male castrated domestic shorthaired cat presented for evaluation of reduced appetite and weight loss of six months duration. A mixed echogenic liver mass is identified, possessing multiple cystlike cavities.

Figure 4B. The postmortem findings from the same cat reveal a multilobulated mass involving the liver parenchyma and arising from the biliary epithelium. The results of the histologic examination of the hepatic lesion were consistent with a biliary cystadenocarcinoma.