What causes cancer?
A. Cancer cells develop because of damage to DNA, a substance in every cell that directs all activity of the cell. Usually when DNA becomes damaged, the body is able to repair it; however, some times it is not repaired and the cell becomes abnormal. Scientists are working to better understand what causes DNA to become damaged. Some people inherit damaged DNA, which accounts for inherited cancers. More often, though, a person’s DNA becomes damaged by exposure to something in the environment or by things people do, like smoking.
At the cellular level, cancer occurs when a cell’s DNA becomes damaged and cannot be repaired. Cancer starts in just one cell, and there are several stages in cancer development — from precancerous changes to malignant tumors. Different cancers develop at different rates. Many different factors can play a role, from genetics (the BRCA genes, for example) to lifestyle habits (such as smoking, diet and sun-tanning) to environmental exposures to harmful substances. Viral and bacterial infections also can lead to certain cancers, such as the hepatitis virus in liver cancer, Helicobacter pylori in stomach cancer, and the HPV virus in cervical cancer. The immune system’s function also is key to controlling or preventing cancer.
