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Liver and Biliary Tract Tumors
Amanda K. Elpiner, DVM, DACVIM (Oncology)

VCA Great Lakes Veterinary Specialists, Cleveland, OH, USA

Etiology/Pathophysiology of hepatobiliary tract tumors help us to make determina­
tions about prognosis for both dogs and cats.
The etiology of hepatobiliary tumors in dogs and cats is
largely unknown although human cases are often linked Hepatocellular Tumors
to infection with the hepatitis virus (B and C) and cirrho­
sis. Cirrhosis, which may be secondary to chronic disease Hepatocellular tumors develop from the hepatocyte.
or alcohol consumption in people, is rare in dogs and a These tumors include hepatocellular adenomas and
viral etiology has not been documented in dogs or cats. hepatocellular carcinomas. Hepatocellular adenomas are
Other theories behind the development of hepatocel­ benign tumors and while they can be found in both dogs
lular carcinoma (HCC) and other hepatobiliary tumors and cats, they are more common in the cat. Hepatocellular
include exposure to chemical carcinogens (aflatoxins or adenomas are typically considered incidental findings
nitrosamines, for example) and chronic infections or and rarely cause clinical signs in affected patients.
inflammatory diseases of the liver. Trematodes are Adenomas can, however, reach a large size, necessitating
thought to be involved in the development of bile duct surgical removal. These tumors are also difficult to
carcinomas in people and this link has also been explored clinically distinguish from a massive HCC without the
in dogs and cats but seems unlikely to be a major cause or aid of a biopsy.
concern. More recently, somatic genetic alterations are Hepatocellular carcinoma is the most common pri­
thought to likely play a role in tumor development, such mary liver tumor in the dog and the second most com­
as mutations in p53, PIK3CA, beta‐catenin, and others mon in the cat. The majority of HCCs are morphologically
which have been documented in people. massive (53–84%) followed by nodular (16–25%) and
There are four main histologic categories of primary diffuse (0–19%) presentations. The left side of the liver is
hepatobiliary tumors in both dogs and cats: hepatocel­ more commonly affected than the right, with over two‐
lular, bile duct, neuroendocrine (carcinoid), and mesen­ thirds of tumors arising from the left lateral, medial, and
chymal (sarcoma). Within in each individual category is papillary process of the caudate lobe. HCCs have the
an array of both malignant and benign tumors. In gen­ ability to metastasize but the likelihood of metastasis is
eral, dogs are thought to be more likely affected by largely based on the morphologic subtype. Massive HCC
malignant tumors whereas cats more often have benign have a low reported rate of metastasis (0–37%) whereas
tumors. the nodular and diffuse subtypes have dramatically
Primary hepatobiliary neoplasms can also be described higher metastatic rates of 93% and 100% respectively.
using three morphologic subtypes: massive, nodular, or Metastasis is most commonly reported to the regional
diffuse. The definition of a massive liver tumor is a large, lymph nodes, peritoneum, and lungs.
solitary mass confined to a single liver lobe; nodular
tumors have discrete nodules scattered throughout mul­ Bile Duct Tumors
tiple liver lobes; diffuse tumors consist of coalescing
nodules within all liver lobes or widespread infiltration There are two primary tumors that can arise from the
of the hepatic parenchyma by neoplastic cells. As we will bile duct epithelium in dogs and cats: bile duct adenomas
discuss further, the histologic and morphologic features and biliary carcinomas. Bile duct adenomas are also called

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical