Malignant primary tumour in the lung. The commonest form of lung cancer originates in the air passages; this is bronchial carcinoma, of which the four commonest forms are pavement cell carcinoma (55 per cent), adenocarcinoma (4 percent), large cell carcinoma (17 per cent) and small cell carcinoma (24 per cent), named after the cells affected. Atmospheric pollution and smoking are linked to all lung conditions, and lung tumours in particular. A direct connection has been shown between lung cancer and the smoking of cigarettes. Cigars and pipe tobacco are less harmful to the lungs because less smoke is inhaled; they do however cause cancers of the mouth and lips. Tobacco smoking became popular at the beginning of this century. The connection between smoking and lung cancer is linked directly to the number of cigarettes smoked and the length of time for which the person has smoked. If nobody smoked at all the occurrence of lung cancer would drop by 90 per cent. The risk is increased by the presence in the lungs of scars caused by tuberculosis or chronic bronchitis. The chances of contracting lung cancer are high in certain occupations because carcinogens are inhaled; the most notorious are substances contained in cigarette smoke, asbestos fibre, chromates, nickel, arsenic, mustard gas and radioactive gases. Men between the ages of 45 and 70 who smoke and have lung trouble are a high risk group; a smoker’s cough can often mask the seriousness of the condition. Symptoms are much like the common cold or bronchitis. Coughing up blood, persistent coughing, a feeling of constriction, hoarseness and chest pain can also point to the presence of a cancer. Sometimes flu-like inflammation symptoms indicate constriction or closure of an air passage by a cancer. Bronchitis which can later degenerate into pneumonia, so-called obstruction pneumonia, occurs behind the point of constriction. The first signs of a cancer can be fatigue, decreased appetite and weight loss. Secondary tumours can present themselves as enlarged lymph nodes, lumps under the skin, or can cause disorders of the central nervous system. Secondary tumours in the bones can cause spontaneous fractures. Lung tumours can be found only in time by chest X-rays. Diagnosis can be confirmed by examining expectorated saliva for malignant cells and by bronchoscopy. Surgery is the only radical treatment for lung cancer; real recovery is possible only if diagnosis is made at an early stage. Much research is being devoted to the possible use of radiation therapy and drugs that inhibit cell division.