In general, cancer is caused by damage to DNA, the genetic material that carries “instructions” to the cells. Normal cells grow, divide, and then die. However, cancer cells are abnormal cells that outlive normal cells. When cells grow in an uncontrollable fashion, they form cancers.
Lung cancer develops when DNA changes causes lung cells to grow abnormally. DNA mutations or defects can turn off genes that suppress tumors or activate oncogenes, which promote cell division. Interestingly, inherited mutations are not thought to cause many lung cancers. Cancer causing mutations usually develop after birth. A faulty DNA repair mechanism renders a person vulnerable to chemicals that may cause cancer.
Lung cancer may also develop in people who inherit a tendency to activate carcinogens. This makes them particularly susceptible to the effects of tobacco smoke and cancer causing industrial chemicals.
Lung cancer usually starts in the lining of the bronchi, which are the two main passageways branching from the trachea or the windpipe, to the lungs. Cancer could also start in the trachea, the smaller passageways from the bronchi known as the bronchioles, or the tiny air sacs at the end of bronchioles known as the alveoli, although these instances do not occur often.
It is believed that lung cancer develops over many years, starting with precancerous changes in the lung that do not take the form of a tumor. Precancerous lesions or early stage lung cancers do not cause symptoms, nor can they be detected by x-ray. However, they can be found when the cells on the lining of the airways are analyzed. These precancerous changes often lead to cancer if left untreated.
Metastasis occurs when cancer cells break away from their original site and affect other parts of the body. Lung cancer may metastasize before it is diagnosed.
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