The histological classification of lung tumors is based upon the 2004 WHO classification. Small cell lung cancer (SCLC) is primarily treated by means of anti-neoplastic chemotherapy, independently of the tumor stage. In resectable stages of non-small cell lung cancer (NSCLC, UICC-stages I and II), complete tumor resection is the aim. Therefore, the distinction between SCLC and NSCLC is still of particular importance. Currently, great interest is focused on the identification of specific therapeutic targets, especially on the inhibition of the epidermal growth factor ruptur (EGFR). Today, malignant lung tumors can also be classified by means of molecular pathology. Subgroups with different prognoses can be identified by gene expression profiling. The expression levels of several genes are associated with sensitivity against certain anti-cancer agents.