How a normal cell becomes cancer
Normal body cells grow, divide, and die in an orderly fashion. During the early years of a person's life, normal cells divide faster to allow the person to grow. After the person becomes an adult, most cells divide only to replace worn-out or dying cells or to repair injuries.
Because cancer cells continue to grow and divide, they are different from normal cells.
Instead of dying, cancer cells outlive normal cells and keep forming new abnormal cells. Another difference between cancer cells and normal cells is that cancer cells can invade (grow into) other tissues. Being able to grow out of control and to invade other tissues makes a cell a cancer cell.
People can inherit damaged DNA, but most of the time DNA damage is caused by something we are exposed to in our environment. Sometimes the cause of the DNA damage is something obvious, like cigarette smoking. But many times no clear cause is found.
A cancer cell has many mistakes in its DNA -- having damage in just one spot does not cause cancer. Even when someone inherits damaged DNA, more mistakes in their DNA are needed before a cancer will develop. Staying away from things that are known to damage DNA (like smoking) as a part of a healthy life style lowers the chance that more DNA damage will take place. This can reduce the risk of cancer -- even in people who have an inherited tendency to get cancer
How cancers grow and spread
In most cases the cancer cells form 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. But sometimes the extra cells in these blood cancers may also form a mass of tissue called a tumor.
Cancer cells often travel to other parts of the body, where they begin to grow and replace normal tissue. This process is called metastasis. It happens when the cancer cells get into the bloodstream or lymph vessels of our body.
But no matter where a cancer may spread, it is always named for the place where it started. For example, breast cancer that has spread to the liver is still called breast cancer, not liver cancer. Prostate cancer that has spread to the bone is metastatic prostate cancer, not bone cancer.
How cancers differ
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.
How common is cancer Cancer is the second leading cause of death in the United States. Nearly half of all men and a little over 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. Often, the sooner a cancer is found and treatment begins, the better are the chances for living for many years.