Liver cancer starts in the liver. The liver is the largest internal organ. The liver keeps you healthy by filtering dangerous substances out of your blood. It also makes enzymes (substances that speed up chemical changes) and bile that help you digest your food and certain factors that help your blood clot.
Liver cancer begins when the cells of the liver grow and divide without stopping. These cells create lumps (masses) called tumors. Liver tumors are often benign, or not cancerous, and do not spread to other tissues or organs. However, some liver tumors can spread to other areas of the body and form new tumors. This is called liver cancer.
About 19,160 men and women will be diagnosed with liver cancer in the United States in 2007, according to the American Cancer Society.
The Liver
The liver is located below your right lung and under your right ribs. It is shaped like a pyramid and has two sections, or lobes. The right lobe is bigger than the left lobe.
Most of the organs in your body get their blood from only one source. But the liver gets blood that is rich in oxygen from the heart through the hepatic artery and blood that is rich in nutrients from the intestines through the portal vein.
The liver contains a large number of blood vessels. This is one reason why cancers that start in other parts of the body often spread to the liver. This article focuses only on cancers that start in the liver and does not deal with liver metastases (cancer cells that started in another part of the body [such as the colon or lungs] and have spread to the liver).
You cannot survive without a liver because it plays so many critical roles, including:
- Collect blood from the intestines
- Filter the blood and break down harmful substances, such as alcohol and drugs
- Make blood clotting factors
- Absorb food from the intestines
- Break down and store food
- Turn nutrients from food into energy or use them to repair and build tissue
- Release bile into the intestine
- Control levels of blood sugar
How Liver Cancer Starts
A liver tumor is a growth of abnormal cells. These cells may be either noncancerous (benign) or cancerous (malignant). Benign liver tumors are made of abnormal cells, but these cells do not spread (metastasize) to other parts of the body. However, the cells in cancerous liver tumors can metastasize, either by spreading directly to tissue or organs near the liver in the abdomen, or by traveling through the bloodstream or lymph system (which helps drain fluid and waste from the body) to other parts of the body.
Most liver cancers start in the liver cells known as hepatocytes. But liver cancer can also start in the small bile ducts, or tubes that carry bile to the gallbladder, and in the liver’s blood vessels. Once a tumor begins in the liver, its cells get the blood they need to grow and divide from the hepatic artery.
When cancer spreads from its original place to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the original tumor. For example, if liver cancer spreads to the lungs, the cancer cells in the lungs are liver cancer cells. The disease is metastatic liver cancer, not lung cancer, and it is treated as liver cancer.
Types of Liver Cancer
There are several types of liver cancer. The most common kinds are:
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Hepatocellular carcinoma (hepatoma, primary liver cancer, hepatic tumor) - This is the most common type of liver cancer in adults, accounting for about 80 percent to 90 percent of all cancers that start in the liver. Hepatocellular carcinoma starts in the liver cells known as hepatocytes. In the United States, most hepatocellular carcinomas start as several small cancer nodules in different parts of the liver. This type of cancer is most common in people with chronic liver damage (cirrhosis). But hepatocellular carcinoma can also start as one tumor that gets bigger and does not spread to other parts of the liver until a later stage.
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Cholangiocarcinoma (intrahepatic cholangiocarcinoma, bile duct cancer) - About 10 percent to 20 percent of liver cancers are cholangiocarcinomas, which start in the thin tubes (small bile ducts) in the liver that carry bile to the gallbladder.
Other, much rarer, liver cancers are:
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Angiosarcoma and hemangiosarcoma - These rare cancers (about 1 percent of all liver cancers) start in the liver’s blood vessels and are most common in people who have been exposed to vinyl chloride or thorium dioxide (Thorotrast). They are also found in people who have been exposed to arsenic or radium, or who have hemochromatosis, an inherited disease. These tumors grow quickly and often spread too far to be removed by surgery by the time they are found.
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Hepatoblastoma - This very rare cancer affects children, usually before age 4. It might be caused by an abnormal gene. Most children with this disease can be treated successfully.
Key Statistics
According to the American Cancer Society, liver cancer is much more common in men than in women; about 13,650 men are expected to be diagnosed with liver cancer in 2007, compared to 5,510 women.
In the last few decades, the percentage of people in the United States who develop liver cancer has increased, although the rate has been relatively stable in recent years. The reason for this increase could be the increase in the number of Americans with viral hepatitis, which is known to cause hepatocellular carcinoma, the most common kind of liver cancer in the United States.
More than 90 percent of people who are diagnosed with liver cancer are 45 to 85 years old and the average age at diagnosis is 65. Liver cancer is much more common in economically developing countries in Africa and East Asia, where it is often the most common type of cancer, than in the United States.
This content has been reviewed and approved by Myo Thant, MD.