Lung cancer is a disease of cancerous condition in lungs. Carcinomas of lung mainly derives from epithelial cells. Lung cancer can metastasize to liver, brain, kidney, etc and hence they are called carcinoma. Lung cancer is caused by mutation in normal working genes:- Epidermal growth factor  receptor (EGFR), which regulates cell proliferation, apoptosis, angiogenesis and also in other genes like CMET and NKX2-1. Two types of cancer can occur in lungs: 1.Non small cell carcinoma which includes squamous cell carcinoma, adenocarcinoma and large cell carcinoma. 2.Small cell lung carcinoma, also called oat cell carcinoma as the cells contain neuroscretory vesicles which releases hormones responsible for parneoplastic syndrome. Lung cancer is the leading cause of death in men than in women.

Any cause for lung cancer is directly associated with mutation in the DNA of the tissue lining the bronchi of lungs.

Smoking is the leading cause for lung cancer. Passive smoking i.e inhaling smoke from someone who is smoking, also called second hand smoking, is the major cause of lung cancer in non-smokers. That's why smoking was banned in India on 2nd October 2008. The length of time a person smokes (as well as the rate of smoking) increases the person's chance of developing lung cancer. 10-15% of lung cancer cases are due to passive smoking. Passive smoking is much harmful than the direct smoking.

Radon gas is produced by Uranium which decays into radium. Radium is a radioactive substance and emits radon gas. The radioactive decay product ionizes the genetic material, causing mutation which turns into a cancerous condition.

Asbestos is the basic cause of cancer for many cancerous condition. This also causes certain mutation, which is responsible for developing cancerous condition.

Many virus like CMV (cytomegalovirus), SV40 (simian virus 40), can cause cancer by affecting the cycle of cell division and inhibit apoptosis, allowing uncontrolled cell division.

90 percent of cases of lung cancer are caused due to cigarette smoking. Exposure to certain substances, such as asbestos, can also lead to the development of lung cancer. Exposure to second-hand smoke and other environmental factors may also be responsible.

The best means to prevent getting lung cancer is to quit smoking. Studies have shown that smokers who quit decrease their risk of lung cancer as compared to those who continue smoking. A good diet consisting of fruits and vegetables, rich in antioxidants and flavonoids helps protect cell's DNA and repair damaged cells.