lung cancerdisease characterized by uncontrolled growth of cells in the lungs. Lung cancer was first described by doctors in the mid-19th century. In the early 20th century it was considered relatively rare, but by the end of the century it was the leading cause of cancer-related death among men in more than 25 developed countries. In the United States it has surpassed breast cancer 21st century lung cancer emerged as the leading cause of cancer deaths worldwide, resulting in an estimated 1.3 million deaths each year. In women lung cancer is the second leading cause of death from cancer among women. This rapid increase is due globally, following breast cancer. In the United States, however, it has surpassed breast cancer. The rapid increase in the worldwide prevalence of lung cancer was attributed mostly to the increased use of cigarettes since following World War I, though increases in environmental air pollution were suspected to have been a contributing factor as well.
Causes and symptoms

Lung cancer occurs primarily in persons between the ages of 45 and 75 years of age. In countries with a prolonged history of cigarette tobacco smoking, between 80 and 90 percent of all cases are caused by smoking. Heavy smokers have a greater likelihood of developing the disease than do light smokers. The risk is also greater for those who started smoking at a young age.

Passive inhalation of cigarette smoke (sometimes called secondhand smoke) is linked to lung cancer in nonsmokers. In the early 1990s it was estimated that passive smoking caused some 2,500 to 3,300 lung cancer deaths each year in the United States, or about 2 percent of all U.S. lung cancer deaths. According to the American Cancer Society, about 3,400 deaths from lung cancer occur each year in nonsmokers in the United States. Other risk factors include exposure to radon gas and asbestos; smokers exposed to these substances run a greater risk of developing lung cancer than do nonsmokers. Uranium and pitchblende miners, chromium and nickel refiners, welders, and workers exposed to halogenated ethers also have an increased incidence, as do some workers in hydrocarbon-related processing, such as coal processors, tar refiners, and roofers. Lung cancer is rarely caused directly by inherited mutations.





Types of lung cancer

Once diagnosed, the tumour’s type and degree of invasiveness are determined. There are two basic forms: small-cell carcinoma, which accounts for 20–25 percent of all cases, and non-small-cell carcinoma, which is responsible for the remainder.

Small-cell carcinoma


Non-small-cell carcinomas


Adenocarcinoma accounts for some 25 to 30 percent of cases worldwide, but it is the most common type of lung cancer in the United States. Cells of adenocarcinoma are cube- or column-shaped, and they form structures that resemble glands and are sometimes hollow. Tumours often originate in the smaller, peripheral bronchi. Symptoms at the time of diagnosis often reflect invasion of the lymph nodes, pleura, and both lungs or metastasis to other organs.







