Overview
What Is Cancer?
Normal body cells grow, divide, and die in a regular way. When a person is young, normal cells divide more rapidly. Then, when the person becomes an adult, cells in most parts of the body divide only to replace worn-out or dying cells and to repair injuries.
Cancer cells, on the other hand, are different from normal cells. The cells themselves are abnormal, and they grow out of control. Instead of dying, they outlive normal cells and continue to form more abnormal cells. Although there are many kinds of cancer, they all start because of out-of-control growth of abnormal cells.
Cancer cells often travel to other parts of the body from the place where they first began to grow out of control. There they begin to grow and replace normal tissue. This process, called metastasis, occurs as the cancer cells get into the body’s bloodstream or lymph vessels. When cells from a cancer like breast cancer spread to another organ like the liver, the cancer is still called breast cancer, not liver cancer.
Cancer cells develop because of damage to DNA. DNA is in every cell and directs all of a cell’s activities. Most of the time when DNA becomes damaged, the body is able to repair it. But in cancer cells, the damaged DNA is not repaired. People can inherit damaged DNA, which explains inherited cancers. Many times, though, a person’s DNA becomes damaged by exposure to something in the environment, like smoking or too much sun.
Cancer usually forms as a tumor, which is an abnormal mass of cells in the body that grow faster than usual and can cause illness. Some cancers, like leukemia, do not form tumors. Instead, these cancer cells affect blood cells and blood-forming organs and circulate through other tissues, where they grow.
It is important to remember that not all tumors are cancerous. Benign (non-cancerous) tumors do not spread to other parts of the body (metastasize) and are almost never life-threatening.
Different types of cancers can behave in ways that are very different from each other. For example, lung cancer and breast cancer are very different diseases. They grow at different rates and respond to different treatments. This means that a person with cancer needs treatment that is aimed at his or her specific kind of cancer.
Cancer is the number-two cause of death in the United States. Half of all men and one-third of all women in the US will develop cancer sometime during their lives. Today, millions of people are living with cancer or have survived cancer. You can reduce your risk of developing most types of cancer by making changes in your lifestyle. These changes include, for example, quitting smoking and eating a better diet. The sooner a cancer is found and treatment begins, the better are the chances that you will live for many more years.