Lung cancer

Lung cancer, also known as lung carcinoma, is a malignant tumor that begins in the lung. Lung cancer is caused by genetic damage to the DNA of cells in the airways, often caused by cigarette smoking or inhaling damaging chemicals. Damaged airway cells gain the ability to multiply unchecked, causing the growth of a tumor. Without treatment, tumors spread throughout the lung, damaging lung function. Eventually lung tumors metastasize, spreading to other parts of the body.

Early lung cancer often has no symptoms and can only be detected by medical imaging. As the cancer progresses, most people experience nonspecific respiratory problems: coughing, shortness of breath, or chest pain. Other symptoms depend on the location and size of the tumor. Those suspected of having lung cancer typically undergo a series of imaging tests to determine the location and extent of any tumors. Definitive diagnosis of lung cancer requires a biopsy of the suspected tumor be examined by a pathologist under a microscope. In addition to recognizing cancerous cells, a pathologist can classify the tumor according to the type of cells it originates from. Around 15% of cases are small-cell lung cancer (SCLC), and the remaining 85% (the non-small-cell lung cancers or NSCLC) are adenocarcinomas, squamous-cell carcinomas, and large-cell carcinomas. After diagnosis, further imaging and biopsies are done to determine the cancer's stage based on how far it has spread.

Treatment for early stage lung cancer includes surgery to remove the tumor, sometimes followed by radiation therapy and chemotherapy to kill any remaining cancer cells. Later stage cancer is treated with radiation therapy and chemotherapy alongside drug treatments that target specific cancer subtypes. Even with treatment, only around 20% of people survive five years on from their diagnosis. Survival rates are higher in those diagnosed at an earlier stage, diagnosed at a younger age, and in women compared to men.

Most lung cancer cases are caused by tobacco smoking. The remainder are caused by exposure to hazardous substances like asbestos and radon gas, or by genetic mutations that arise by chance. Consequently, lung cancer prevention efforts encourage people to avoid hazardous chemicals and quit smoking. Quitting smoking both reduces one's chance of developing lung cancer and improves treatment outcomes in those already diagnosed with lung cancer.

Lung cancer is the most diagnosed and deadliest cancer worldwide, with 2.2 million cases in 2020 resulting in 1.8 million deaths. Lung cancer is rare in those younger than 40; the average age at diagnosis is 70 years, and the average age at death 72. Incidence and outcomes vary widely across the world, depending on patterns of tobacco use. Prior to the advent of cigarette smoking in the 20th century, lung cancer was a rare disease. In the 1950s and 1960s, increasing evidence linked lung cancer and tobacco use, culminating in declarations by most large national health bodies discouraging tobacco use.

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.