Background: The exceptionally high rate of second primary cancers among patients with oral and pharyngeal cancers is well recognized, yet there has been limited epidemiologic study of risk factors for second tumors.
Purpose: To evaluate the relation of smoking and alcohol consumption to the development of second cancers among this high-risk patient group, we conducted a nested case-control study.
Methods: A total of 1090 patients enrolled in a 1984-1985 population-based, case-control study of oral cancer in four areas of the United States were followed through June 1989 for the occurrence of second primary cancers. Information on tobacco and alcohol consumption was obtained from the original interviews and was updated by follow-up interviews obtained for 80 case patients with second cancers and 189 sex-, study area-, and survival-matched cancer patients free of second cancers (control subjects).
Results: Tobacco smoking and alcohol drinking each contributed to risk of second cancers, with the effects of smoking more pronounced than those of alcohol. The odds ratios (ORs) for smoking (adjusted for alcohol) rose with duration and intensity of smoking and were strongest for tumors of the aerodigestive tract (oral cavity, pharynx, esophagus, larynx, and lungs), with ORs reaching 4.7 (95% confidence interval [CI] = 1.4-16) among smokers of 40 or more cigarettes per day for 20 or more years. Current smokers as of the baseline survey experienced a fourfold increased risk of a second aerodigestive tract cancer relative to nonsmokers and former smokers. No reduction in risk was associated with cessation of smoking or drinking at or after the index diagnosis, although the short median interval (27 months) between tumor diagnoses limited observation of the effects due to recent cessation. Risk was significantly reduced, however, 5 years after smoking cessation. Among drinkers, second cancer risk was greatest for beer intake, with an OR for a second aerodigestive tract cancer of 3.8 (95% CI = 1.2-12) for 15 or more beers per week.
Conclusions: Oral and pharyngeal cancer patients with the highest intakes of tobacco and alcohol are the ones most prone to develop second primary cancers.
Implications: Avoidance of tobacco smoking and alcohol drinking is the most desirable way not only to prevent primary oral cancers, but also to reduce risk of second cancers of the aerodigestive system.