Malignant tumour of the lung .
Four major types (squamous-cell carcinoma, adenocarcinoma, large-cell carcinoma, and small-cell carcinoma) have roughly equal prevalence. Most cases are due to long-term cigarette smoking . Heavy smoking and starting smoking earlier in life increase the risk. Passive inhalation ("secondhand smoke") is linked to lung cancer in nonsmokers. Other risk factors include exposure to radon or asbestos . Symptoms, including coughing (sometimes with blood), chest pain, and shortness of breath, seldom appear until lung cancer is advanced, when treatment with surgery, chemotherapy, and radiation or some combination of the three is less effective. Most patients die within a year of diagnosis.