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Last Edited: 10/8/2009


Cancer is a group of many related diseases characterized by the uncontrolled growth and spread of abnormal cells within the body. Normally, cells divide and grow in a controlled, orderly way, making new cells to keep our bodies healthy and repair damage. When abnormal cells continue dividing out of control, they form a tumor, which can be benign or malignant.

Benign tumors are not cancer and are rarely life-threatening. Malignant tumors are cancer and, if not treated, may result in death. Cells in a malignant tumor do not function normally and they divide in an uncontrolled way, often invading and damaging nearby tissues and organs. Cancer cells from a malignant tumor can also break away and spread (metastasize) through the bloodstream or the lymphatic system to other parts of the body.

Most cancers are named for the organ or type of cell in which they began. For example, cancer that begins in the breast is called "breast cancer." The place in the body where a cancer begins is called the primary (original) site. When cancer spreads from its original location to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary tumor. For example, if lung cancer spreads to the brain, the cancer cells in the brain are actually lung cancer cells, therefore, the disease is called metastatic lung cancer (cancer that has spread from the lung). A wealth of detailed information on specific cancer types is available at the National Cancer Institute website.

Cancer can strike a person at any age. In California, more children under 14 years of age die from cancer than from any other disease. Among adults, cancer occurs more frequently with advancing age. About 15 million Californians, or two of every five now living, will eventually be diagnosed with cancer. Despite this seemingly discouraging statistic, the estimated relative five-year survival rate for cancer is 62%. Many cancers can be cured if detected early and treated promptly. Still others, especially those related to tobacco and heavy alcohol use, can be prevented entirely.

The causes of most cancers are unknown. Cancers may be caused by characteristics in our genes, things we are exposed to in our environment or a combination of both these factors. Recently, much public concern has focused on identifying exposures in our environment that may contribute to our risk of getting cancer. This focus has centered on a desire to decrease cancer incidence by educating people about cancer risk factors and reducing or preventing their exposure to known carcinogens (cancer-causing chemicals or physical forces, such as radiation). In an effort to achieve both these ends, the Environmental Health Investigations Branch (EHIB) conducts epidemiological studies of possible environmental risk factors for cancer. The Branch also investigates suspected cancer excesses in small areas (sometimes referred to as "cancer clusters") and provides surveillance indicators through the California Environmental Health Tracking web portal.





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