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.
Canine hepatic sarcomas
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
Although various primary sarcomas (leiomyosarcoma, fibrosarcoma, myxosarcoma, liposarcoma) have been reported, the most common
sarcomas to affect the hepatic parenchyma are hemangiosarcoma (Figure 2) and histiocytic sarcoma.2,4 Therapy for these two sarcomas may depend on determining whether the tumor arises primarily from the liver or whether it
is metastatic, which may be suggested by the size of the hepatic lesion. Surgical excision of a primary hepatic hemangiosarcoma
or excisional biopsy of suspected hepatic metastases from a primary splenic hemangiosarcoma may be considered and should be
followed by systemic chemotherapy with a doxorubicin-based protocol.
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
Although neoplastic processes have been documented in cats as young as 2 years old, hepatobiliary tumors are primarily a disease
of older cats (average 12 years). Hepatobiliary tumors may be classified as either malignant or benign, with malignant tumors
more commonly arising in younger cats (average 9 years) compared with benign tumors (average 14.5 years) (Table 2).38 In contrast to dogs in which most hepatobiliary tumors are malignant, up to 65% of primary hepatobiliary tumors in cats
are benign (Figure 3).38-40 More than 50% of feline hepatobiliary tumors are incidental findings at surgery or necropsy.38
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
The average age of cats with biliary adenocarcinomas and cystadenocarcinomas (Figures 4A & 4B) is 13.3 to 14.5 years, and male cats are overrepresented (Table 2).41-43 Despite a palpable abdominal mass or hepatomegaly in about half of affected cats, elevations in liver enzyme activities
and bilirubin concentrations are uncommon (Table 4).38,40-42 Although many cats may present for clinical signs attributable to the hepatobiliary system, 38% of cats are asymptomatic.42
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.
Definitive treatment recommendations for cats with biliary adenocarcinoma or cystadenocarcinomas remain to be determined,
but consider surgical resection if anatomically feasible. In two case series, surgical excision resulted in minimal complications,
and no local recurrence was observed in the 12 to 44 months of postsurgical follow-up.43,44 Based on these limited studies, surgical excision may provide prolonged disease-free intervals and high quality-of-life
scores in cats with biliary adenocarcinomas and carcinomas of the biliary tract.
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