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Liver Cancer.Cancer of the liver can be divided into two distinct categories, primary or secondary, depending upon the site of origin. Primary liver cancer originates in the liver itself and is relatively rare in the United States, accounting for only 1 to 2 percent of all cancers. About 90 percent of all primary liver cancers in the United States are hepatocellular carcinomas, meaning they arise in the liver cells. About 7 percent start in the liver's bile ducts, and the remaining are angiosarcomas, which are very rare but of growing importance because they are associated with polyvinylchlo-ride (PVCs) and other similar industrial toxins. The liver, which weighs up to four pounds in an adult, is the body's largest internal organ and one of its most complex It performs numerous biochemical functions, including detoxifying alcohol and other potentially harmful chemicals. Bile, cholesterol, digestive enzymes, and complex proteins are among the vital substances manufactured in the live:. It serves as a storehouse for glycogen, which is converted into blood sugar (glucose) to provide fuel for ail the body's cells. It is also essential in a number of metabolic processes and serves as a storehouse for vitamins A and D.
Secondary liver cancer is a result of metastases from a cancer elsewhere in the body, frequently the breast, lung, or colon. It is quite common, since many cancers that are not cured by surgical removal or other treatments will spread to the liver.
The pattern of incidence for liver cancer is quite different in other parts of the world, particularly some of the developing countries. In Africa and parts of Asia, primary liver cancer is one of the most common malignancies. In Ethiopia, for example, it accounts for 20 percent of all malignancies, and in some developing countries primary liver cancer may be the leading cause of cancer death.
The age at which the cancer is likely to develop also varies geographically. In the United States, most patients with hepatocellular carcinoma are of late middle age or older. In Africa, the disease is more likely to strike during young adulthood or early middle age, and somewhat later in Asia.
The reasons for these geographic differences are unknown, but a number of factors that increase the risk of liver cancer have been identified. Cirrhosis, either from alcoholism or from other diseases such as viral hepatitis, is a major predisposing factor for liver cancer. In the United States, a person with cirrhosis is forty times more likely to develop primary liver cancer than a person with a normal liver, and 30 to 70 percent of all patients with hepatocellular cancer also have cirrhosis. It should be noted that cirrhosis can develop from several causes other than alcoholism, including viral and (less commonly) parasitic infections, nutritional deficiencies, and hemochromatosis, a disease characterized by excessive iron deposits in the body tissue. Statistically, the cirrhosis of hemochromatosis, followed closely by that caused by viral hepatitis, are the most likely to evolve into cancer.
Hemochromatosis is a relatively rare metabolic disorder; in contrast, viral hepatitis is fairly common. In some parts of the world, particularly the developing countries of Africa and Asia, viral hepatitis is endemic and a major precursor of liver cancer. Still, most people who have viral hepatitis recover completely and do not go on to develop liver cancer. In addition, the recent development of a vaccine against viral hepatitis is considered a major step in preventing the primary liver cancer that is associated with this disease.
A number of environmental toxins also have been linked to an in creased risk of liver cancer. Since the liver performs so many biochemical functions, including detoxifying potentially harmful chemicals, it is exposed to a large number of environmental carcinogens. Aflatoxin, which is derived from some molds; azo compounds, a family of nitrogen compounds; and Thorotrast, a contrast substance once used in X-ray examinations but which has been discontinued, are among the substances linked to an increased risk of liver cancer. Oral estrogens, particularly those used in birth control pills, have been associated with a number of cases of benign liver tumors that can cause acute bleeding problems and, in some instances, the eventual development of cancer. The number of such cancers is small, however, and the risk appears to be minimal for most women except those with a history of liver disease.
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