Lung cancer, also known as bronchial carcinoma, since about 98–99% of all lung cancers are carcinomas, is a malignant lung tumor characterized by uncontrolled cell growth in tissues of the lung. Lung carcinomas derive from transformed, malignant cells that originate as epithelial cells, or from tissues composed of epithelial cells. Other lung cancers, such as the rare sarcomas of the lung, are generated by the malignant transformation of connective tissues (i.e. nerve, fat, muscle, bone), which arise from mesenchymal cells. Lymphomas and melanomas (from lymphoid and melanocyte cell lineages) can also rarely result in lung cancer.
In time, this uncontrolled growth can spread beyond the lung – either by direct extension, by entering the lymphatic circulation, or via the hematogenous, bloodborne spread – the process called metastasis – into nearby tissue or other, more distant parts of the body. Most cancers that start in the lung, known as primary lung cancers, are carcinomas. The two main types are small-cell lung carcinoma (SCLC) and non-small-cell lung carcinoma (NSCLC). The most common symptoms are coughing (including coughing up blood), weight loss, shortness of breath, and chest pains.
The vast majority (85%) of cases of lung cancer are due to long-term tobacco smoking. About 10–15% of cases occur in people who have never smoked. These cases are often caused by a combination of genetic factors and exposure to radon gas, asbestos, second-hand smoke, or other forms of air pollution. Lung cancer may be seen on chest radiographs and computed tomography (CT) scans. The diagnosis is confirmed by biopsy, which is usually performed by bronchoscopy or CT-guidance.
The major method of prevention is the avoidance of risk factors, including smoking and air pollution. Treatment and long-term outcomes depend on the type of cancer, the stage (degree of spread), and the person's overall health. Most cases are not curable. Common treatments include surgery, chemotherapy, and radiotherapy. NSCLC is sometimes treated with surgery, whereas SCLC usually responds better to chemotherapy and radiotherapy.
Worldwide in 2020, lung cancer occurred in 2.2 million people and resulted in 1.8 million deaths. It is the most common cause of cancer-related death in men and second-most common in women after breast cancer. The most common age at diagnosis is 70 years. In the United States, five-year survival rate is 20.5%, while in Japan it is 41.4%. Outcomes typically are worse in the developing world.
The October 1996 edition of the journal Science reported the first actual scientific evidence from the cell biology level to link smoking to lung cancer. While many scientists have long been convinced by statistical studies and animal experiments that tobacco causes cancer, a statistical association was not in itself absolute proof. Until now the tobacco industry has always maintained that "the causal link remains to be established." In the published paper, researchers from the University of Texas M.D. Anderson Cancer Centre in Houston and the Beckman Research Institute of the City of Hope in Duarte in California, studied the effects of a cigarette-smoke ingredient on a gene known as p53. The scientists say a chemical found in cigarette smoke has been found to cause genetic damage in lung cells that is identical to the damage observed in many malignant tumors of the lung.
Since 1955, the incidence of lung cancer has risen in all EEC/EU countries (with Denmark and the UK at the top), against a falling rate for all cancers. Lung cancer is by far the commonest cause of cancer for men and smoking is the biggest single cause, accounting for 30% of all cancer and almost all lung cancer. Lung cancer rates in women have increased in all European countries since 1955.
Between 2% and 5% of lung cancer cases can be attributed to radon accumulating indoors.