A wide range of genetic and phenotypic abnormalities have been identified in lung cancer. However, only a few are known to have an impact on patient outcome and thus may influence choice of therapy. Biologic and molecular factors known in this regard include the epidermal growth factor family and its receptors, markers of neuroendocrine differentiation in non-small cell lung cancer, and mutations of the ras gene family. None of these factors, however, dan be considered a standard for selection of patients for therapy until additional information is gleaned from ongoing prospective studies.