Lung cancer is the malignant transformation and expansion of lung tissue, and is the most lethal of all cancers worldwide, responsible for 1.2 million deaths annually. It is a leading cause of cancer death in men and women in the United States. Cigarette smoking causes most lung cancers. The more cigarettes you smoke per day and the earlier you started smoking, the greater your risk of lung cancer. High levels of pollution, radiation and asbestos exposure may also increase risk. There are many types of lung cancer. Each type of lung cancer grows and spreads in different ways and is treated differently. Treatment also depends on the stage, or how advanced it is. Treatment may include chemotherapy, radiation and surgery. Lung cancer that originates in the cells of the lungs is called primary lung cancer; however, cancer may also spread to the lung from other parts of the body. Metastatic cancers spread to the lungs most commonly from the breast, colon, prostate, kidney, thyroid gland, stomach, cervix, rectum, testis, bone, and skin (melanoma). More than 90% of primary lung cancers start in the bronchi such lung cancer is called bronchogenic carcinoma. The specific types of lung cancer are small cell carcinoma, squamous cell carcinoma, large cell carcinoma, and adenocarcinoma. The last three types of lung cancer are often referred to as nonsmall cell lung cancers. Alveolar cell carcinoma originates in the small air sacs of the lung (alveoli). Although alveolar cell carcinoma can occur at a single site, it often develops simultaneously in more than one area of the lung. Less common lung tumors are bronchial carcinoid (which may be cancerous or noncancerous), chondromatous hamartoma and sarcoma. Lymphoma is a cancer of the lymphatic system; it may start in the lungs or spread to them.
Lung cancer is the rapid growth of abnormal cells in the lung. It can start anywhere in the lungs and affect any part of the respiratory system . When we breathe in, the lungs take in oxygen, which our cells need to live and carry out their normal functions. When we breathe out, the lungs get rid of carbon dioxide, which is a waste product of the body's cells. Cancers that begin in the lungs are divided into two major types, non-small cell lung cancer and small cell lung cancer, depending on how the cells look under a microscope.
