Sputum analysis: non-invasive early lung cancer detection

Lung cancer is the leading cause of cancer-related deaths over the world, characterized by a very high mortality rate. Molecular technique development tries to focus on early detection of cancers by studying molecular alterations that characterize cancer cells. Worldwide lung cancer research has focused on an ever-increasing number of molecular elements of carcinogenesis at genetic, epigenetic and protein levels. The non-invasiveness is the characteristic that all clinical trials on cancer detection should have. Abnormal chest imaging and/or non-specific symptoms are initial signals of lung cancer that appear in an advanced stage of disease. This fact represents the cause of the low 5-year survival rate: over 90% of patients dying within 5 years of diagnosis. Since smokers have higher quantity of sputum containing exfoliated cells from the bronchial tree, and the sputum represents the most easily accessible biological fluid and its collection is non-invasive, analysis of this sample represents a good area of research in early lung cancer diagnosis. Continued cigarette smoking is the cause of chronic obstructive pulmonary disease (COPD), with an estimated attributable risk factor exceeding 80% in smoking affected individuals. Lung cancer is found in 40-70% of patients with COPD, particularly in severe disease, and it is a common cause of death in these patients. A large prospective trial of almost half a million non-smokers showed as lung cancer is also common in patients with COPD who have never smoked. This review describes issues related to early lung cancer screening using non-invasive methods.