Mesothelioma is fairly rare. There are about 2,000-3,000 new cases per year in this country. Most people who get mesothelioma are over 65 years old. Men are much more likely than women to get this disease.

Although rare, this is a serious disease. It is often advanced before symptoms appear, so the outlook is not as good as it is for cancers that are found earlier. The average survival time is about 1 to 2 years.

Mesothelioma is fairly rare. There are an estimated 2,000 to 3,000 new cases of mesothelioma each year in the United States. The incidence of mesotheliomas in the United States increased from 1970 to 1990 and then stabilized. It may now be decreasing. Most of the past increase in cases, as well as the recent decrease in cases, has been in men. The rate, although lower, has been fairly steady for women. In European countries, the rate of mesotheliomas is still increasing.

Mesothelioma is rare in people under age 55. Its incidence increases with age. Three-fourths of people with mesothelioma are over 65 years old. The disease affects men 5 times more often than women. Mesothelioma is less common in African Americans than in white Americans.

Mesothelioma is a serious disease. By the time the symptoms appear and cancer is diagnosed, the disease is often advanced. The average survival time is about 1 year. The 5-year relative survival rate is around 10%, but this rate has been slowly improving.

The 5-year survival rate refers to the percentage of patients who live at least 5 years after their cancer is diagnosed. Many of these patients live much longer than 5 years after diagnosis, and 5-year rates are used to produce a standard way of discussing prognosis. Five-year relative survival rates do not include patients dying of other diseases and are considered to be a more accurate way to describe the prognosis for patients with a particular type and stage of cancer. That means that relative survival only talks about deaths from mesothelioma. Of course, 5-year survival rates are based on patients diagnosed and initially treated more than 5 years ago. They may no longer be accurate. Improvements in treatment result in a more favorable outlook for recently diagnosed patients.

Cancer develops when cells in a part of the body begin to grow out of control. Although there are many kinds of cancer, they all start because of out-of-control growth of abnormal cells.

Normal body cells grow, divide, and die in an orderly fashion. During the early years of a person’s life, normal cells divide more rapidly until the person becomes an adult. After that, cells in most parts of the body divide only to replace worn-out or dying cells and to repair injuries.

Because cancer cells continue to grow and divide, they are different from normal cells. Instead of dying, they outlive normal cells and continue to form new abnormal cells.

Cancer cells develop because of damage to DNA. This substance is in every cell and directs all activities. Most of the time when DNA becomes damaged the body is able to repair it. In cancer cells, the damaged DNA is not repaired. People can inherit damaged DNA, which accounts for inherited cancers. More often, though, a person’s DNA becomes damaged by exposure to something in the environment, like smoking.

Cancer usually forms as a tumor. Some cancers, like leukemia, do not form tumors. Instead, these cancer cells involve the blood and blood-forming organs and circulate through other tissues where they grow.

Often, cancer cells travel to other parts of the body where they begin to grow and replace normal tissue. This process is called metastasis. Regardless of where a cancer may spread, however, it is always named for the place it began. For instance, breast cancer that spreads to the liver is still called breast cancer, not liver cancer.

Not all tumors are cancerous. Benign (noncancerous) tumors do not spread (metastasize) to other parts of the body and, with very rare exceptions, are not life threatening.

Different types of cancer can behave very differently. For example, lung cancer and breast cancer are very different diseases. They grow at different rates and respond to different treatments. That is why people with cancer need treatment that is aimed at their particular kind of cancer.

Cancer is the second leading cause of death in the United States. Half of all men and one third of all women in the United States will develop cancer during their lifetimes. Today, millions of people are living with cancer or have had cancer. The risk of developing most types of cancer can be reduced by changes in a person’s lifestyle, for example, by quitting smoking and eating a better diet. The sooner a cancer is found and treatment begins, the better are the chances for living for many years.