What are the genetic changes related to lung cancer ?
Cancers occur when genetic mutations build up in critical genes, specifically those that control cell growth and division or the repair of damaged DNA. These changes allow cells to grow and divide uncontrollably to form a tumor. In nearly all cases of lung cancer, these genetic changes are acquired during a person's lifetime and are present only in certain cells in the lung. These changes, which are called somatic mutations, are not inherited. Somatic mutations in many different genes have been found in lung cancer cells.  Mutations in the EGFR and KRAS genes are estimated to be present in up to half of all lung cancer cases. These genes each provide instructions for making a protein that is embedded within the cell membrane. When these proteins are turned on (activated) by binding to other molecules, signaling pathways are triggered within cells that promote cell growth and division (proliferation).  Mutations in either the EGFR or KRAS gene lead to the production of a protein that is constantly turned on (constitutively activated). As a result, cells are signaled to constantly proliferate, leading to tumor formation. When these gene changes occur in cells in the lungs, lung cancer develops.  Mutations in many other genes have each been found in a small proportion of cases.  In addition to genetic changes, researchers have identified many personal and environmental factors that expose individuals to cancer-causing compounds (carcinogens) and increase the rate at which somatic mutations occur, contributing to a person's risk of developing lung cancer. The greatest risk factor is long-term tobacco smoking, which increases a person's risk of developing lung cancer 20-fold. Other risk factors include exposure to air pollution, radon, asbestos, or secondhand smoke; long-term use of hormone replacement therapy for menopause; and a history of lung disease such as tuberculosis, emphysema, or chronic bronchitis. A history of lung cancer in closely related family members is also an important risk factor; however, because relatives with lung cancer were likely smokers, it is unclear whether the increased risk of lung cancer is the result of genetic factors or exposure to secondhand smoke.