Background: The goals of this study were to measure the impact of cigarette smoking on cancer incidence and to determine the attributable risk of cancer due to smoking.
Methods: A cigarette smoking history was obtained from 8006 Japanese-American men examined from 1965 through 1968. After 22 years, 1389 incident cases of cancer were identified. There were 212 men with lung cancer; 202 with oral, esophageal, laryngeal, pancreatic, renal, ureteral, or bladder (oral-bladder) cancer; and 975 with cancer at other sites.
Results: Current smokers at time of examination had a higher incidence than nonsmokers for each of the three cancer site categories. Eighty-five percent of lung cancer cases diagnosed among current and never smokers can be attributed to cigarette smoking. The attributable risks were 46%, 16%, and 29%, respectively, for oral-bladder cancers, other cancers, and all cancers combined. In turn, the corresponding attributable risks were 60%, 26%, 13%, and 21% in comparing current smokers with past smokers.
Conclusions: Current smokers can greatly reduce their risk of cancer, especially lung cancer, if they quit smoking.