Causes

A malignant lung tumor forms from one or more original cancer cells.

Smoking causes most cases of lung cancer because tobacco contains some of the most toxic substances known to human beings. Cyanide, arsenic and carbon monoxide are all carcinogens, known to induce mutations in cells that trigger cancer. Other environmental toxins known to cause lung cancer include radon and asbestos.

With the cells under attack from toxins, mutations start occurring. Then, after years of accumulated injuries, one cell - the parent cancer cell - acquires the unique feature of cancer, the ability to grow and divide more rapidly than neighboring cells. Descendents of the original parent form a lung tumor.

Cancers that begin in the lungs can be divided into two main types: small cell lung cancer (about 20 percent), and non-small cell lung cancer (80 percent). The cell type or microscopic appearance of the tumor cells determines the type of cancer present and the recommended treatment. Small cell lung cancers grow rapidly, and metastasize early. They respond better to chemotherapy and radiation treatment than non-small cell lung cancers, which grow more slowly.

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