What is Lung Cancer?
The lungs are two sponge-like organs found in the chest cavity. The right lung has three sections, called lobes. The left lung has two lobes. It is smaller because the heart takes up more room on that side of the body. The lungs bring air in and out, taking in oxygen and getting rid of carbon dioxide gas, a waste product of the body.
The lining, which surrounds the lungs and helps to protect them and to facilitate the sliding motion during respiration, is called the pleura. The chest cavity is called the pleural cavity. The trachea (windpipe) brings air down into the lungs. It divides into tubes called the bronchi, which divide into smaller branches called the bronchioles. At the end of the bronchioles are tiny air sacs known as alveoli.
Most lung cancers start in the lining of the bronchi. But cancer can also begin in the trachea, bronchioles or alveoli. Lung cancers are thought to develop over a period of many years. First, there may be areas of precancerous changes in the lung. These changes do not form a mass or tumor. They cannot be seen on an x-ray, and they do not cause symptoms. But, researchers are studying new tests to detect precancerous changes by analysis of cells in sputum and by viewing the lining of the airways through a bronchoscope. However, if these precancerous changes progress to true cancer, malignant (cancerous) cells begin to grow. The cancer cells may produce chemicals that cause new blood vessels to form nearby. These new blood vessels nourish the cancer cells, which can continue to grow and form a tumor large enough to see on x-rays. Cells from the cancer can break away from the original tumor and spread to other parts of the body. This process is called metastasis. Lung cancer is a life-threatening disease because it often spreads even before it is detected by x-rays.
Common Types of Lung Cancer
Lung cancer is usually divided into two major types. The first type is small cell lung cancer (SCLC). The second type is non-small cell lung cancer NSCLC. Sometimes a lung cancer may have characteristics of both types. This is called mixed small cell/large cell carcinoma.
Small cell lung cancer (SCLC)
About 20% of all lung cancers are SCLC. This type of cancer is named for the size of the cancer cells that are apparent when viewed under a microscope. These cells can multiply quickly and form large tumors, and can spread to lymph nodes and other organs such as the bones, brain, adrenal glands and liver. This type of cancer often starts near the bronchi and toward the center of the lungs. Small cell lung cancer is almost always caused by smoking. It is very rare for someone who has never smoked to have small cell lung cancer. Other names for SCLC are oat cell lung carcinoma and small cell undifferentiated carcinoma.
Non-small cell lung cancer (NSCLC)
This type of cancer accounts for almost 80% of lung cancers. It includes three sub-types. The cells in these sub-types differ in size, shape and chemical make-up.
Squamous Cell Carcinoma: About 30% of all lung cancers are squamous cell carcinomas. They are associated with a history of smoking and tend to be found centrally, near a bronchus.
Adenocarcinoma: This type of cancer accounts for about 40% of all lung cancers. It is usually found in the outer region of the lung. People with one type of adenocarcinoma, known as bronchioloalveolar carcinoma, tend to have a better outlook (prognosis) than other types of lung cancers in this group, although often these tumors may arise in more than one site.
Large-Cell Undifferentiated Carcinoma: This type of cancer accounts for about 10% of lung cancers. It may appear in any part of the lung, and it tends to grow and spread quickly, resulting in a poor prognosis. When it has spread to other areas, no cell type has a worse prognosis. More large cells are found at an advanced stage, but the patient’s prognosis is determined by the stage at presentation, not the cell type.