Lung cancer is the leading cause of death from cancer in Western countries. For improved diagnosis and refined therapeutical approaches it is of major importance to understand by what mechanisms carcinoma of the lung develop. The analysis of primary lung cancer revealed specific chromosomal alterations and allelic losses of the short arm of chromosome 3. Genetic aberrations have been observed in proto-oncogenes such as H-ras, K-ras, C-myc and raf-1 as well as in the tumor suppressor genes Rb and p53. Rearrangement of rlf and elevated expression in certain lung tumors have also been reported. The development of lung cancer also involves the altered activation of genes coding for growth factors such as TGF beta 2 and certain growth factor receptor genes such as c-erbB-2, HEK2 and FGFR-4.