Normal human cells grow, divide, and die in an orderly fashion. During the early years in a person's life, normal cells divide more rapidly until the person becomes an adult. From adulthood, cells in most parts of the body divide only to replace worn-out or dying cells and to repair injuries.
Cancer Cells v. Normal Cells
Since cancer cells continue to grow and divide, they are distinct from normal cells. Rather than dying, they outlive normal cells and continue to form new abnormal cells. Cancer cells develop because of damage to DNA. Usually, 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. This explains how cancer can be inherited. However, in most cancer cases, a person's DNA becomes damaged by exposure to something in the environment such as smoking and other toxic substances.
How Cancer Forms
Cancer typically forms as a tumor. Some cancers (e.g., leukemia) do not form tumors. Instead, these cancer cells involve the blood and blood-forming organs which spread through other tissues where they grow. Cancer cells often 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. Thus, breast cancer that spreads to the liver is still called breast cancer, not liver cancer.
Benign Tumors v. Malignant Tumors
Not all tumors are cancerous. Benign (non-cancerous) tumors do not spread (or metastasize) to other parts of the body and are rarely life threatening. Malignant tumors are those that metastasize and are cancerous.
Different Types of Cancer
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.
Importance of Diagnosing Cancer Early
The sooner cancer is diagnosed and treated, the better the patient' prognosis. Finding cancer early often means treatment while it is still small and is less likely to have spread to other parts of the body. This usually means a better chance for a cure, particularly if initial treatment is surgery. For this reason, routine check ups can be critically important to diagnosing caner early. Aside from routine checkups, many doctor recommend that patients should report any of the following signs to their doctor immediately: extreme fatigue, a mass on the breast, unusual skin formations or discolorations, unexplained pain, and any other abnormalities.
Some cancers may be detected by before symptoms occur. For this reason, the American Cancer Society and other health groups recommend cancer related check ups and specific tests for cancer for people who do not have symptoms. Additional information on early detection tests may found in the American Cancer Society Guidelines for Early Detection of Cancer.