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Types of Cancer > Gastrointestinal Cancers > Liver Cancer (Hepatoma) > Overview
Liver Cancer: The Basics
S.Jack Wei, MD
Affiliation:
The Abramson Cancer Center of the University of Pennsylvania
Last Modified: October 21, 2004
What is the liver?
The liver is the largest solid organ of the body and is located on the right side of the abdomen just beneath the right diaphragm. Surrounding organs include the gall bladder (located just behind the liver), the small intestine, part of the colon (large intestine), the right kidney, and the head of the pancreas. The liver is triangular in shape and is divided into a right and left lobe, the right lobe being the larger of the two. It provides several important functions to the body including:
- Filtering the blood to remove and process toxins
- Synthesizing and excreting bile, which is important in processing fat from our diet
- Helping regulate blood sugar (glucose) levels
- Producing factors that play an important role in blood clotting
The liver is a very vascular structure, containing a large number of blood vessels, and receives blood through two separate systems: the hepatic artery and the portal vein. Blood from the abdomen and lower body flows through the liver where it is processed. It then proceeds to the inferior vena cava and ultimately empties into the heart. In large part, due the vascular nature of the liver, it is a very common site to which cancers from other areas of the body to spread (also known as metastasis )
What is liver cancer?
Normally, cells in the body will grow and divide to replace old or damaged cells. This growth is highly regulated, and once enough cells are produced to replace the old ones, normal cells will stop dividing. Tumors occur when there is an error in this regulation and cells continue to grow uncontrolled. Tumors of the liver occur when there is an error in the regulation of growth of any of the cells in the liver, including the liver cells themselves ( hepatocytes ), the bile duct cells, or the blood vessels within the liver.
Tumors can either be benign or malignant. Although benign tumors grow uncontrolled, then do not break off and spread beyond where they started and do not invade into surrounding tissues. Malignant tumors, however, will invade and damage other tissues around them. They can also gain the ability to break off from where they started and spread to other parts of the body (metastasize), usually through the blood stream or through the lymphatic system where the lymph nodes are located. Over time, the cells of a malignant tumor become more abnormal and appear less like normal cells. This change in the appearance of cancer cells is called the tumor grade , and cancer cells are described as being well-differentiated, moderately-differentiated, poorly-differentiated, or undifferentiated. Well-differentiated cells are quite normal appearing and resemble the normal cells from which they originated. Undifferentiated cells are cells that have become so abnormal that, we cannot tell what types of cells they started from.
There are a number of benign liver tumors. Hemangiomas are the most common benign tumor of the liver, and occur when a benign, blood-filled tumor forms within the liver. Other benign tumors include adenomas (benign tumors of the hepatocytes) and focal nodular hyperplasia (a localized growth of several types of liver cells). Although these tumors do not invade surrounding tissues or metastasize, it is often difficult to tell the difference between benign and malignant tumors on radiographic imaging.
In addition to being a common site of metastasis for cancers from other sites in the body, primary liver cancers can arise from within the liver itself. Cancer arising from the hepatocytes is known as hepatocellular carcinoma (HCC) . It is the most common type of primary liver cancer and accounts for around 70% of all liver cancers. Cancers that arise from the bile ducts within the liver are known as cholangiocarcinomas and represent 10-20% of all liver cancers. These cancers can arise from the bile ducts within the liver (known as intrahepatic cholangiocarcinomas) or from in the bile ducts as they lead away from the liver (known as extrahepatic cholangiocarcinomas). Other types of rare cancers can occur within the liver. These include hemangiosarcomas (malignant blood-filled tumors) and hepatoblastoma (a rare cancer that develops in very young children).
What causes liver cancer and am I at risk?
Each year, there are approximately 17,000-19,000 cases of liver cancer in the United States with 14,000-15,000 people dying of the disease each year. Liver cancer is much more common in other areas of the world, particularly in sub-Saharan Africa and Southeast Asia . Worldwide, liver cancer is the fifth most common cancer with a half a million people afflicted each year. The number of people who develop liver cancer is increasing both abroad and in the United States .
There are a number of risk factors that are associated with liver cancer. In the United States , the most common risk factor for liver cancer is liver cirrhosis . Sixty to eighty percent of patients presenting with liver cancer have some signs of cirrhosis. Cirrhosis results from scar formation within the liver, most commonly due to chronic alcohol use . Chronic infection with hepatitis C virus (HCV) is also a common cause of liver cancer in the United States . Worldwide, other risk factors, such as chronic infection with hepatitis B virus (HBV) and aflatoxin B1 food contamination are more common. Aflatoxin is a toxic chemical that is produced by a fungus commonly seen in tropical regions. Presence of the fungus on food in these regions leads to chronic exposure to the toxin, resulting in an increased risk of developing liver cancer. Tobacco use has also been associated with increased risk; however, it is not as strong of a risk factor as alcohol-induced liver cirrhosis. Other environmental factors include exposure to thorium dioxide (Thorotrast, a contrast agent previously used for radiographic imaging that is no longer used), vinyl chloride , arsenic exposure , and use of anabolic steroids . Several inherited diseases can increase the risk of liver cirrhosis, and therefore increase the risk of developing liver cancer. These disease include hemochromatosis (where the body absorbs and stores too much iron), Wilson 's disease (where the body inappropriately retains too much copper), and alpha-1-antitrypsin deficiency (a deficiency in a key enzyme that can lead to emphysema of the lung and cirrhosis of the liver). Patients with a family history of liver cancer may also be at increased risk. Finally, males are about twice as likely to develop liver cancer as females. This may be due to a genetic predisposition of males for liver cancer, but may also be due to the fact that males are more likely to be exposed to the risk factors discussed above.