Lung cancer is a disease in which the cells of the lung tissues grow uncontrollably and form tumors. There are two kinds of lung cancers, primary and secondary. Primary lung cancer starts in the lung itself. Primary lung cancer is divided into small cell lung cancer and non-small cell lung cancer, depending on how the cells look under the microscope. Secondary lung cancer is cancer that starts somewhere else in the body (for example, the breast or colon) and spreads to the lungs.

Small cell cancer was formerly called oat cell cancer, because the cells resemble oats in their shape. About a fourth of all lung cancers are small cell cancers. It is a very aggressive cancer and spreads to other organs within a short time. It is generally found in people who are heavy smokers. Non-small cell cancers account for the remaining 75% of lung cancers...