Most experts agree that lung cancer is attributable to inhalation of carcinogenic pollutants by a susceptible host. Who is most susceptible? Any smoker over the age of 40, especially if they began smoking before the age of 15, have smoked 20 or more for 20 years, or worked with or near asbestos. Two other factors also increase susceptibility: exposure to carcinogenic industrial and air pollutants (asbestos, uranium, arsenic, nickel, iron oxides, chromium, radio active dust, and coal dust.) and familial susceptibility.

Because early lung cancer usually produces no symptoms, the disease is often in an advanced stage when first diagnosed. Late stage signs are: with epidermoid and small cell carcinoma; smokers cough, hoarseness, wheezing, dyspnea, hemoptysis and chest pain. With adenocarcinoma and large cell carcinoma; fever, weakness, weight loss, anorexia and shoulder pain. In addition, hormone production which regulates various body functions may also be affected.