**3. Molecular mechanism of lung cancer**

Molecular aberrations in oncogenes, proto-oncogenes as well as tumor suppressor genes have been recognized broadly in the pathogenesis of lung cancer. Gain of function mutation of oncogenes, and loss of function mutation of tumor suppressor genes result in the accumulation of multiple genetic abnormalities over a period of time that act by causing cellular alterations such as loss of function mutation of TP53, Rb genes is common in small-cell carcinoma whereas gain of function mutation of genes encoding tyrosine kinase receptors is seen in adenocarcinoma as depicted in **Figure 1**. Accumulation of multiple genetic abnormalities forms an initiating step for tumor progression. Some of the genetic alterations involved in lung cancer progression are discussed as follows.
