Lung cancer is a kind of cancer that starts as a growth of cells in the lungs. Lung cancer is the leading cause of cancer deaths worldwide. People who smoke have the greatest risk of lung cancer. The risk of lung cancer increases with the length of time and number of cigarettes smoked. Quitting smoking, even after smoking for many years, significantly lowers the chances of developing lung cancer. Lung cancer also can happen in people who have never smoked. 

Lung cancer happens when cells in the lungs develop changes in their DNA. A cells DNA holds the instructions that tell a cell what to do. In healthy cells, the DNA gives instructions to grow and multiply at a set rate. The instructions tell the cells to die at a set time. In cancer cells, the DNA changes give different instructions. The changes tell the cancer cells to make many more cells quickly. Cancer cells can keep living when healthy cells would die. This causes too many cells. 

The cancer cells might form a mass called a tumor. The tumor can grow to invade and destroy healthy body tissue. Cancer cells can break away and spread to other parts of the body. When cancer spreads, its called metastatic cancer. 

Smoking causes most lung cancers. It can cause lung cancer in both people who smoke and in people exposed to secondhand smoke. Lung cancer happens in people who never smoked or been exposed to secondhand smoke. In these people, there may be no clear cause of lung cancer. 

TYPES OF LUNG CANCER

Lung cancer is divided into two major types based on the appearance of the cells under a microscope. 

Two general types of lung cancer include :

1. SMALL CELL LUNG CANCER - usually happens only in people who have smoked heavily for years. It is less common than non small cell lung cancer.
2. NON SMALL CELL LUNG CANCER - includes several types of lung cancer. It includes squamous cell carcinoma, adenocarcinoma and large cell carcinoma. 

SYMPTOMS

Lung cancer typically does not cause symptoms early on. Symptoms of lung cancer usually happen when the disease is advanced. 

Signs and symptoms that happen in and around the lungs include :

• Cough that doesn't go away
• Chest pain
• Coughing up blood
• Hoarseness
• Shortness of breath
• Wheezing
• Bone pain
• Headache
• Losing weight
• Loss of appetite
• Swelling in the face or neck