Lung cancer is the leading cause of cancer death in the United States. Each year, about 154,900 Americans die of lung cancer. Cigarette smoking causes the great majority of lung cancer cases.

At present, there is no way to confidently predict variations in lung cancer risk among current and previous smokers. As a result, neither individuals nor their doctors have a reliable way to determine whether they should be screened for lung cancer. Lung cancer screening is usually done by a computed tomography (CT) scan. But CT scans can produce false positive results, requiring further evaluation or biopsy of an abnormality that will eventually be found harmless.

But what if lung cancer risk among current and previous smokers was found to vary, and if individual risk could be determined? This information could potentially help target individuals who would benefit most from screening, thereby reducing unnecessary biopsies, complications, cost, and anxiety in smokers and ex-smokers at low risk.

In a study published in the March 19, 2003 Journal of the National Cancer Institute , researchers from Memorial Sloan-Kettering Cancer Center and the Fred Hutchinson Cancer Research Center found that the 10-year risk of developing lung cancer can be predicted based on a person’s age, sex, and smoking history.

About the Study

The researchers collected data from participants of the Carotene and Retinal Efficacy Trial (CARET), which had enrolled 18,314 people. Of these, 14,254 were heavy smokers (defined as smoking at least one pack per day for 20 years) aged 50–69 years, who were still smoking or had quit within six years of enrollment. Another 4060 participants were men, aged 45–69 who had a history of asbestos exposure and were either current smokers or had quit within 15 years of enrollment. The study began in 1985 and the participants have been followed annually by mail.

For this study, researchers analyzed the smoking behavior and smoker characteristics of 18,172 of the original participants to create a mathematical equation that could predict the likelihood that an individual would develop lung cancer within the next ten years.

The Findings

As of February 2002, 1070 of the study subjects had been diagnosed with lung cancer.

The following factors were the best predictors of lung cancer risk:

  • Duration of smoking
  • Average number of cigarettes smoked per day
  • Duration of abstinence from smoking
  • Age

The researchers found a large amount of variation in 10-year lung cancer risk in this group of current and former smokers. It ranged from 0.8% (less than 1 in 100) for a 51-year old woman who smoked one pack per day for 28 years before quitting nine years earlier to 15% (1 out of 7) for a 68-year old man who has smoked two packs per day for 50 years and continues to smoke.

One limitation of the model developed in this study is that it only applies to people aged 50 and older who have smoked for 25 or more years.

How Does This Affect You?

By using the risk assessment tool developed by these researchers, individuals and their doctors should be able to better weigh the risks and benefits of having a CT scan to screen for lung cancer. The researchers suggest that the risk assessment tool might also help researchers select the truly high-risk individuals for their studies, allowing them to better assess the value of screening and prevention strategies. It is currently not known, for example, when and how often CT scans should be recommended.

But the most important benefit of this tool could be the effect that it has on smokers. If a smoker is confronted with his or her actual risk of developing lung cancer, it might provide enough of an incentive to quit. And because the tool predicts the risk of lung cancer in two scenarios—quitting and not quitting—it can illustrate how dramatically quitting reduces risk. On the flip side, the tool could provide some peace of mind for former smokers by illustrating how their risk will continue to fall as long as they stay former smokers.