ORAL-CANCER AND MOUTHWASH USE - EVALUATION OF THE EPIDEMIOLOGIC EVIDENCE

BACKGROUND: An association between mouthwash use and cancer of the oropharynx has been the focus of many epidemiologic studies. PURPOSE: To critically review the methodology of studies of this association. METHODS: Studies were identified through a computerized MEDLINE search of English-language publications from 1976 to 1994. Eligible studies were independently reviewed, and specific criteria were applied to assess issues in the design, analysis, and results of the studies. Methodologic criteria were used that define a case-control study of acceptable epidemiologic quality: (1) histologic confirmation of cancer; (2) use of incident cases; (3) population-based cases; (4) equal exclusions of controls; (5) population-based controls; (6) exposure to mouthwash use before the cancer diagnosis; and (7) adjustments or restrictions for tobacco, alcohol, or both. RESULTS: Seven case-control studies were identified. The odds ratios for these studies ranged from a protective effect (0.82 for any use of mouthwash) to an elevation in risk (2.5 at the highest exposure). Two studies had significant unadjusted odds ratios for the risk of oral cancer, Of the three studies with data on women adjusted for tobacco and alcohol use, one was statistically significant, and none of the three similar studies in men was significant (although one was close), The five studies with data on female nonsmokers, nondrinkers, or both had odds ratios ranging from 1,1 to 3.16 (only one study was significant at the p = 0.05 level), and the four studies with similar data on men were not significant, Two studies met only two of the methodologic criteria, three studies met three, one met four, and one met all seven, CONCLUSIONS: Few of the available studies on mouthwash use and risk of subsequent oropharynx cancer adhere to basic methodologic principles of case-control design. Neither the data for the overall association nor the analysis in patients without other clinical risk factors support a link between mouthwash use and oral cancer.