When the researchers analyzed the 23,000 mutations, they found distinctive patterns associated with the cocktail of carcinogens present in cigarette smoke. The DNA sequence of the cancer cells also revealed that the cells had attempted to repair their smoke-damaged DNA using two mechanisms, but the cells were only partially successful.

Cigarette smoke deposits hundreds of chemicals into the airways and lungs. The longer one smokes and the more cigarettes smoked each day, the higher the risk of developing lung cancer and mutations.

"By applying the same approach to other cancers not associated with cigarette smoking, including the very large group of people who develop lung cancer but have never smoked, it may be possible to discern which carcinogens play a role in those other cancers as well," Dr. Gazdar said.

Dr. Minna added that the research methods used to analyze the cancer cells represented a technological tour de force.

"The data demonstrate the power of whole-genome sequencing to untangle the complex mutational signatures found in cancers induced by cigarette smoke," Dr. Minna said. "In addition, the protein product of the CHD7 gene now becomes a new marker for early diagnosis and also for potentially targeted therapy."

Lung cancer is the leading cause of cancer-related deaths worldwide, developing in more than a million patients annually. People who smoke are 10 to 20 times more likely to get lung cancer or die from lung cancer than people who do not smoke. SCLC represents 15 percent of these cases and is associated with early metastasis, relapse after initial response to chemotherapy and less than a two-year survival rate.