The most common and acknowledged cause of lung cancer is smoking, specifically high levels of carcinogens, which is one of the constituents enclosed in cigarettes. Another cause of lung cancer is inhalation of radon gas, which is a gas generated when radioactive materials are broken down by radium. Asbestos is another major cause of cancer, it can be found in walls and building materials however asbestos is illegal in many countries now because of the strong link with cancer.Lung cancer can also be inherited from family members, this is known as genetic predisposition.There are two focal kinds of lung cancer: primary lung cancer and secondary lung cancer. Primary lung cancer starts in the lungs while secondary lung cancer begins someplace else in the body and metastasizes, then reaches the lungs. Secondary lung cancer is not as common as primary lung cancer.Furthermore, there is an uncommon type of lung cancer known as the pleural mesothelioma. It occurs when mesothelioma develops in the pleural.There are several factors affecting the growth of lung cancer, such as, amount of exposure to carcinogens, how many progressive/ regressive cells there are and what type of cancer it is. Cancer is diagnosed in different stages to calculate the severity of the cancer.Stage 0 cancer, also known as CIS, Carcinoma in situ consists of cells with the abnormal changes found in cancer cells, but this is not known as ‘cancer’ because it has not spread to the outer tissues. 11 stage 1, this is when the cancerous cells have traveled into the tissue by breaking down the basement membrane, forming a lump in the tissue. Stage 2 and 3 mean the cancer has become aggressive, grew larger and grown into nearby tissues. Lastly, stage 5, also known as advanced or metastatic cancer, means the cancer has spread to other parts of your body.