Cancer arising from lung tissue is called lung cancer. Normal lung tissue is a soft sponge like tissue filled with air pockets (alveoli). When there is an uncontrolled and abnormal growth of cells due to genetic defect or repeated cell injury in them, cancer occurs and solid masses are formed that may clog up the airways causing cough or breathing difficulty or erode into the supplying blood vessels and cause blood in phlegm. Since lung is also a common site for metastatic cancer from other sites in the body, a distinction needs to be made whether the cancer arose primarily from lung or spread to it from another primary lesion in the body.
Lung Cancer is largely classified into two main types based on the cancer′s appearance under a microscope viz. Small Cell Carcinoma which accounts for only 20% of the total lung cancers and Non-small Cell Lung Cancer (NSCLC) which accounts for 80% of lung cancers.