Lung cancer is the main reason for cancer deaths in men & women throughout the world. Main cause for cancer deaths in women is breast cancer has surpassed from lung cancer. In the year 2007 about 160 to 390 individuals were projected to die in United States from lung cancer, which was much higher number of deaths caused by breast, colorectal & prostate cancer combined.

Cancer occurs, when normal cells start growing with a normal control and generates mass or tumor which is different from surrounding tissues. Tumors are horrific because they take nutrients, oxygen & space from healthy cells.
Most lung tumors are malignant. This means that they invade and destroy the healthy tissues around them and can spread throughout the body.

• The tumors can also spread to nearby lymph nodes or through the bloodstream to other organs. This process is called metastasis.
• When lung cancer metastasizes, the tumor in the lung is called the primary tumor, and the tumors in other parts of the body are called secondary tumors or metastatic tumors.
  
  
  
  

Some lung tumors are metastatic from cancers elsewhere in the body. The lungs are a common site for metastasis. If this is the case, the cancer is not considered to be lung cancer. For example, if prostate cancer spreads via the bloodstream to the lungs, it is metastatic prostate cancer (a secondary cancer) in the lung and is not called lung cancer.
Lung cancers are usually divided into two main groups that account for about 95% of all cases.

• The division into groups is based on the type of cells that make up the cancer.
• The two main types of lung cancer are characterized by the cell size of the tumor when viewed under the microscope. They are called small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). NSCLC includes several subtypes of tumors.
• SCLCs are less common, but they grow more quickly and are more likely tometastasize than NSCLCs. Often, SCLCs have already spread to other parts of the body when the cancer is diagnosed.
• About 5% of lung cancers are of rare cell types, including carcinoid tumor, lymphoma, and others.