Canine Liver/Bile Tumors
Primary hepatobiliary tumors (tumors of the liver and bile ducts) are rare in dogs, accounting for less than 2% of all canine neoplasms. They most often occur in older animals with no breed or sex predilection. Most neoplasms are malignant and no causative agents have been identified, however, the detoxification role of the liver may make the hepatobiliary system more susceptible to carcinogenic compounds. Hepatobiliary tumors are divided into one of four types: hepatocellular tumors, bile duct tumors, neuroendocrine tumors (carcinoids), and primary sarcomas. Hepatobiliary tumors have a moderate to high metastatic potential depending on the type (20-60% for hepatocellular carcinoma, 80% for biliary carcinomas, and 90% for carcinoids). However, low-grade tumors metastasize in <20-25% even though the multifocal disease may be present for hepatocellular carcinoma. Metastasis most commonly affects the regional lymph nodes, lungs, and the lining of the abdominal cavity.
Most dogs will present with clinical signs of liver disease at the time of diagnosis (anorexia, increased thirst/urination, vomiting, lethargy) and a mass or fluid is often noted on abdominal palpation. Full staging should be performed including bloodwork, which may reveal elevated liver enzymes, increased bile acids, clotting abnormalities, and/or a low blood glucose (studies have shown that as many as 38% of dogs may be hypoglycemic secondary to a hepatobiliary tumor). Chest radiographs should be performed to look for lung metastasis and abdominal radiographs and ultrasound should be performed to characterize the involvement and guide therapy (surgical resection for localized disease vs. chemotherapy for widespread involvement). An ultrasound-guided aspirate can also be obtained to differentiate between the different types of hepatobiliary tumors but a biopsy may be necessary for a definitive diagnosis. At the time of diagnosis, the tumor can be diffuse (diffusely present throughout all liver lobes), nodular (several nodules in multiple liver lobes), or massive (a large mass confined to one liver lobe). Advanced imaging techniques such as MRI have been shown to provide additional diagnostic information regarding benign vs. malignant lesions and to document widespread metastasis that may not be noted on ultrasound.
Hepatocellular tumors are most often hepatocellular carcinoma (HCC), which represents ~50% of all liver tumors. The benign version, hepatocellular adenoma is less common. Most dogs with HCC will present with a large mass confined to one liver lobe, making surgical resection the treatment of choice. Although there are few studies in the veterinary literature on this tumor, the median survival time with surgery alone is roughly 1.5 years. This means that 50% of the dogs lived longer and 50% lived shorter. Many oncologists will recommend follow-up chemotherapy due to the metastatic potential of this tumor. Recently there has been some investigation into using metronomic chemo for narrowly or incompletely removed HCC. Metronomic chemo is designed to be anti-angiogenic, or against new blood vessel formation. Cancer cells must acquire new blood vessels for oxygenation and nourishment in order to grow into a sizable mass. The goal of starting metronomic chemo is to prevent these blood vessels from forming to feed any microscopic cancer cells. This may thereby delay disease recurrence and improve the long-term prognosis. Metronomic chemo may be used for multifocal tumors, although typically standard chemo would be used in these cases.
Bile duct tumors are most often biliary carcinomas (BC), representing 20-40% of malignant liver tumors, followed by biliary adenomas. Biliary carcinomas can occur within the body of the liver or within the bile ducts and gallbladder and can be nodular or diffuse at the time of diagnosis. Unfortunately, the invasive nature of this tumor makes surgical resection difficult if not impossible and systemic chemotherapy is often not rewarding.
Carcinoids are almost always diffuse and highly metastatic. They are rarely able to be surgically removed unless it is a rare case that has a solitary mass. Chemo is generally poorly effective in treating these tumor types since they tend to be resistant to most chemo agents, however, treatment with newer chemo drugs such as Palladia (off-label) have shown promising results in anecdotal reports. Primary hepatic sarcomas are uncommon and are most commonly hemangiosarcoma or leiomyosarcoma. Hemangiosarcoma is an aggressive neoplasm originating from blood vessels. Metastasis (to the lungs or other intra-abdominal sites) is already present in a majority of cases at the time of diagnosis. Surgical resection of the primary tumor (when possible) and systemic chemotherapy is recommended.
One newer investigational form of therapy for localized, inoperable hepatic tumors is the used of chemoembolization. This is a process whereby a catheter is fed directly to the affected liver lobe and chemotherapy is deposited followed by a “blocking” agent to essentially cause that lobe to become dormant. This may prevent further progression of cancer outside of this lobe.