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The liver is made up mainly of cells called hepatocytes. It also has other types of cells, including cells that line its blood vessels and cells that line small tubes in the liver called bile ducts. The bile ducts carry bile from the liver to the gallbladder or directly to the intestines.

You cannot live without your liver. It has many important functions:

• It breaks down and stores many of the nutrients absorbed from the intestine that your body needs to function. Some nutrients must be changed (metabolized) in the liver before they can be used for energy or to build and repair body tissues.
• It makes most of the clotting factors that keep you from bleeding too much when you are cut or injured.
• It delivers bile into the intestines to help absorb nutrients (especially fats).
• It breaks down alcohol, drugs, and toxic wastes in the blood, which then pass from the body through urine and stool

The different types of cells in the liver can form several types of malignant (cancerous) and benign (non-cancerous) tumors. These tumors have different causes, are treated differently, and have a different prognosis (outlook).

Primary liver cancer

A cancer that starts in the liver is called primary liver cancer. There is more than one kind of primary liver cancer.

Hepatocellular carcinoma (HCC)

This is the most common form of liver cancer in adults.

Hepatocellular cancers can have different growth patterns:

• Some begin as a single tumor that grows larger. Only late in the disease does it spread to other parts of the liver.
• A second type seems to start as many small cancer nodules throughout the liver, not just a single tumor. This is seen most often in people with cirrhosis (chronic liver damage) and is the most common pattern seen in the United States.

Doctors can classify several subtypes of HCC. Most often these subtypes do not affect treatment or prognosis (outlook). But one of these subtypes, fibrolamellar, is important to recognize. It is rare, making up less than 1% of HCCs and is most often seen in women younger than age 35. Often the rest of the liver is not diseased. This subtype tends to have a better outlook than other forms of HCC.

Most of the rest of this content refers only to hepatocellular carcinoma and is called liver cancer. 

Intrahepatic cholangiocarcinoma (bile duct cancer)

About 10% to 20% of cancers that start in the liver are intrahepatic cholangiocarcinomas. These cancers start in the cells that line the small bile ducts (tubes that carry bile to the gallbladder) within the liver. Most cholangiocarcinomas, however, actually start in the bile ducts outside the liver.

Although the rest of this information is mainly about hepatocellular cancers, cholangiocarcinomas are often treated the same way. For more detailed information on this type of cancer, see Bile Duct Cancer.

Angiosarcoma and hemangiosarcoma

These are rare cancers that begin in cells lining the blood vessels of the liver. People who have been exposed to vinyl chloride or to thorium dioxide (Thorotrast) are more likely to develop these cancers (see Liver cancer risk factors). Some other cases are thought to be caused by exposure to arsenic or radium, or to an inherited condition known as hereditary hemochromatosis. In about half of all cases, no likely cause can be identified.

These tumors grow quickly and are usually too widespread to be removed surgically by the time they are found. Chemotherapy and radiation therapy may help slow the disease, but these cancers are usually very hard to treat. These cancers are treated like other sarcomas. For more information, see Soft Tissue Sarcoma.

Hepatoblastoma

This is a very rare kind of cancer that develops in children, usually in those younger than 4 years old. The cells of hepatoblastoma are similar to fetal liver cells. About 2 out of 3 children with these tumors are treated successfully with surgery and chemotherapy, although the tumors are harder to treat if they have spread outside the liver.

Secondary liver cancer (metastatic liver cancer)

Most of the time when cancer is found in the liver it did not start there but has spread (metastasized) from somewhere else in the body, such as the pancreas, colon, stomach, breast, or lung. Because this cancer has spread from its original (primary) site, it is called a secondary liver cancer. These tumors are named and treated based on their primary site (where they started). For example, cancer that started in the lung and spread to the liver is called lung cancer with spread to the liver, not liver cancer. It is also treated as lung cancer.

In the United States and Europe, secondary (metastatic) liver tumors are more common than primary liver cancer. The opposite is true for many areas of Asia and Africa.

For more information on liver metastases from different types of cancer, see specific cancer types, as well as Advanced Cancer.

Benign liver tumors

Benign tumors sometimes grow large enough to cause problems, but they do not grow into nearby tissues or spread to distant parts of the body. If they need to be treated, the patient can usually be cured with surgery.

Hemangioma

The most common type of benign liver tumor, hemangiomas, start in blood vessels. Most hemangiomas of the liver cause no symptoms and do not need treatment. But some may bleed and need to be removed with surgery.

Hepatic adenoma

Hepatic adenoma is a benign tumor that starts from hepatocytes (the main type of liver cell). Most cause no symptoms and do not need treatment. But some eventually cause symptoms, such as pain or a lump in the abdomen (stomach area) or blood loss. Because there is a risk that the tumor could rupture (leading to severe blood loss) and a small risk that it could eventually develop into liver cancer, most experts will usually advise surgery to remove the tumor if possible.

Using certain drugs may increase the risk of getting these tumors. Women have a higher chance of having one of these tumors if they take birth control pills, although this is rare. Men who use anabolic steroids may also develop these tumors. Adenomas may shrink when these drugs are stopped.

Focal nodular hyperplasia

Focal nodular hyperplasia (FNH) is a tumor-like growth made up of several cell types (hepatocytes, bile duct cells, and connective tissue cells). Although FNH tumors are benign, they might cause symptoms. It can be hard to tell them apart from true liver cancers and doctors sometimes remove them when the diagnosis is unclear.

Both hepatic adenomas and FNH tumors are more common in women than in men.