How Does Lung Cancer Develop?

Smoking is the major risk factor for lung cancer

Lung cancer is one of the most cancers in United States. Every year, there are 160,000-180,000 new cases of lung cancer. 80-90% of lung cancer cases are due to smoking. The risk of lung cancer in current smokers is 10-20 times higher than in people that have never smoked. The risk of lung cancer in smokers depends on how long a person smokes and how many cigarettes she smokes a day. Smoking cessation reduces the risk of lung cancer. The risk of lung cancer at 5 years after quitting smoking is half of what it was before quitting.
Other forms of tobacco use like pipes or cigars are also associated with an elevated risk of lung cancer.
A small fraction of lung cancer cases are due to exposure to radon or second-hand smoking.

Exposure to carcinogens leads to mutations in lung cells.

According to the American Cancer Society, cigarette smoke contains more than 4000 chemicals, 80 of which are known carcinogens (substances that cause cancer). Radon is also a carcinogen. Other airborne carcinogens found in office and at home are arsenic, asbestos, and chromium.
Exposure of lung tissues to carcinogens causes gene mutations that affect each cell's ability to maintain normal cell growth and division. Continued exposure increases the number of cells affected. Eventually, the mutated cells keep dividing beyond control and form a tumor.

Most lung cancers are found at later stages.

Symptoms of lung cancer include chronic cough, persistent wheezing, persistent lung infections or pneumonia, chest pains, difficulty in swallowing, coughing up blood. Lung cancer can also metastasize and form new tumors in other organs.

There are two major types of lung cancer, namely, non-small cell and small cell. Small cell lung carcinomas (SCLC) originate from Feyrter cells in the bronchus and are less frequent in comparison to non-small cell.

Treatment for small cell lung carcinomas are mainly chemotherapy and radiation, as surgery was shown to have no effect on survival. The 5-year survival rate for SCLC is very low, 15-30% for limited stage SCLC and 0-2% for advanced stage SCLC.

Surgery in combination with chemotherapy and radiation have been shown to work for non-small cell lung carcinomas (NSCLC). If detected early, the 5-year survival rate can be as high as 60-80%. However, most lung cancers are detected at later stages, when the tumor has started to invade the neighboring tissues and lymph nodes. The 5-year survival rate for NSCLC at later stages are only 5-20%.

Regular chest x-rays or CT scans are highly recommended for people who smoked for many years or are exposed to radon or asbestos.

Resources

• National Institue of Health, Lung Cancer