The DNA abnormalities that lead to the development of cancer may occur in either of two types of genes—those that promote cell growth or those that suppress cell growth.
Both types function normally and in a coordinated way during human growth and development. But genetic changes can cause the normally well regulated growth-promoting mechanisms within a cell to become uncontrolled.
Oncogenes One of the more exciting discoveries in the past is that some of our normal genes may be activated in various ways and transformed into genes capable of changing a normal cell into a cancer cell. These activated and cancer-causing genes are called oncogenes .
We all carry unactivated or normal forms of oncogenes in our chromosomes . In the unaltered state, these genes are referred to as proto-oncogenes. They stay dormant or perform useful functions throughout our lives unless they are stimulated, mutated or otherwise activated to become oncogenes. Once activated, they can work with other genes to transform a normal cell into a cancer cell. This is believed to be a multi-step process in which the DNA undergoes an initial change, then further changes complete the process of malignant transformation. Fortunately, a single genetic change is not sufficient to cause cancer.
A proto-oncogene is activated to an oncogene by a metabolic defect that occurs inside the cell. This defect may spontaneously arise with aging or by exposure to a physical or chemical agent (a carcinogen) that can damage chromosomes or DNA. Radiation in the form of sunlight or x-rays, chemicals and other environmental
