Lung cancer is the leading cause of cancer deaths in both women and men in the United States and throughout the world. Lung cancer has surpassed breast cancer as the leading cause of cancer deaths in women. In the United States in 2007, 160,390 people were projected to die from lung cancer, which is more than the number of deaths from colorectal, breast, and prostate cancer combined. Only about 2% of those diagnosed with lung cancer that has spread to other areas of the body are alive five years after the diagnosis, although the survival rates for lung cancers diagnosed at a very early stage are higher, with approximately 49% surviving for five years or longer.
Cancer occurs when normal cells undergo a transformation that causes them to grow and multiply without the normal controls. The cells form a mass or tumor that differs from the surrounding tissues from which it arises. Tumors are dangerous because they take oxygen, nutrients, and 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 to metastasize 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.
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