Cancer is regarded as an "acquired multigene disease". Hence, diagnosis and treatment of cancer based on molecular pathogenesis are potentially superior to conventional methods. There have been many reports concerning the significance of molecular markers in the diagnosis and therapy of lung cancer over the last 10 years. Those include identification of people more susceptible to lung cancer by SNP analysis, early diagnosis or molecular staging based on highly sensitive PCR technology, or

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... lar markers as prognosticators or predictors of chemosensitivity. However, there is no evidence, established by good quality clinical trials, of the superiority of molecular-based approaches to conventional ones for the better outcome of patients with lung cancer. Recently, owing to the Human Genome Project and the advent of DNA chip technology, it has become possible to perform comprehensive analysis of cancer by expression profiling. It is now the focus of interest of many investigators to accurately predict patient prognosis or sensitivity to treatment, although it has been difficult to do so by analysis of single or limited numbers of gene (s). Iressa is a newly introduced molecular-targeted drug for lung cancer and it specifically inhibits EGFR tyrosine kinase. Although it is not possible to predict which patients would benefit from Iressa treatment, it will soon be possible in the near future. For the future development of this field, it is important to accumulate specimens of good quality from patients who are treated under the same protocol as well as to develop more sophisticated methodology.