Lung Cancer That Is Not Attributable to Smoking

To the Editor. — The report by the Centers for Disease Control, Atlanta, Ga, on mortality attributable to cigarette smoking¹has led us to look further at respiratory cancers to see how much of these diseases might not be attributable to smoking. The smoking-attributable fraction for bronchogenic cancer can be developed from published data²on the proportion of active smokers, the proportion of quit smokers, and the amounts smoked. From the data of Dorn and Hammond,³the relative risk for smokers is roughly given by 1 plus half the number of cigarettes smoked per day. Assuming that the average quit smoker is at one third the excess risks of a continuing smoker, we find the following smoking-attributable fractions for lung cancer based on 1965 smoking patterns: These smoking-attributable fractions imply that for recent lung cancer mortality⁴(1984 data, allowing for roughly a 20-year latent period), the