Mass screening of at risk middle aged smokers has not been successful at detecting lung cancers at an early curable stage. Attempts using both sputum cytology and chest radiographs have been tried but have not proved cost effective. Early cancers are often not visible on chest radiographs. Morphological examination of cells exfoliated into sputum is too coarse a method of detecting the early changes of neoplasia. More promising is the possibility of staining exfoliated cells for genetic changes which long precede changes which can be detected on cytological examination. Genetic probes have been developed for a number of the common oncogenes seen in lung cancer. The exfoliation of cells into sputum gives a ready vehicle for detecting changes deep within the bronchial tree. Unfortunately once abnormal cells are found in sputum, finding their exact source is a more difficult matter. Laser light can illuminate areas of metaplasia but frequently this is so widespread throughout the bronchial tree that determining the segment which is likely to develop an invasive tumour is not possible.

As the human genome has been more completely unravelled a number of genetic polymorphisms and cytogenetic variations have come to be associated with a risk for lung cancer. The combination of polymerase chain reaction and oligo-nucleotide array technology may make it possible to inexpensively screen blood samples from a suspected at risk population. Hopefully the finding of a high risk chromosomal pattern or the detection of genetically abnormal cells in sputum will encourage patients to stop smoking and also help target other screening technologies and help select patients for chemoprevention.