The liver continuously filters blood that circulates through the body, converting nutrients and drugs absorbed from the digestive tract into readytouse chemicals. The liver performs many other important functions, such as removing toxins and other chemical waste products from the blood and readying them for excretion. Because all the blood in the body must pass through it, the liver is unusually accessible to cancer cells traveling in the bloodstream.
The liver can be affected by primary liver cancer, which arises in the liver, or by cancer which forms in other parts of the body and then spreads to the liver. Most liver cancer is secondary or metastatic, meaning it started elsewhere in the body. Primary liver cancer, which starts in the liver, accounts for about 2% of cancers in the U.S., but up to half of all cancers in some undeveloped countries. This is mainly due to the prevalence of hepatitis, caused by contagious viruses, that predisposes a person to liver cancer. In the U.S., primary liver cancer strikes twice as many men as women, at an average age of 67.
Because the liver is made up of several different types of cells, several types of tumors can form there. Some of these are benign (noncancerous), and some are cancerous and can spread to other parts of the body (metastasize). These tumors have different causes and are treated differently. The outlook for health or recovery depends on what type of tumor you have.