Lung cancer is malignancy of the lungs and is the leading cause of cancer deaths for both men and women in the United States and Canada. About 90 percent of all lung cancer occurs in current or former smokers.

It is estimated that 164,000 new cases of lung cancer are diagnosed annually in the United States and an estimated 157,000 people die from the disease each year. Approximately 20,600 new cases of lung disease are diagnosed in Canada annually, and the disease causes 17,700 deaths a year.

There are four main types of lung cancer, which tend to arise in different parts of the lung and differ in characteristics and behavior. Squamous cell carcinoma accounts for 20 percent of all lung cancer. It often begins toward the central part of the lung in the bronchial tubes, which are the major airways that lead into the lungs. About 40 percent of lung cancers are adenocarcinomas, which are cancers that originate on the outer edges of the lungs and under the lining of the bronchial tubes. Small-cell carcinoma spreads more rapidly than any other type of lung cancer. It is characterized by small cells that may be shaped like either oat grains or rods and makes up about 20 percent of lung cancer cases. Ten percent of all cases are large-cell carcinomas, cancers characterized by large, abnormal cells that usually begin along the outer edges of the lung.

Lung cancer often metastasizes, or spreads, through the bloodstream or lymphatic system to other tissues. More than 50 percent of people newly diagnosed for lung cancer already show signs of cancer elsewhere in the body. Conversely, some cancers detected in the lung are actuall

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