Cigarette smoking and the incidence of cervical intraepithelial neoplasia, grade III, and cancer of the cervix uteri.

The relation between cigarette smoking and cervical intraepithelial neoplasia, grade III (CIN III), and cervical cancer was examined among a cohort of 6,812 women in Tromsö, Norway, between 1980 and 1989. During the 52,844 person-years of observation, 185 incident cases (177 women with CIN III and eight with cervical cancer) were recorded in the regional pathology registry. The age-adjusted incidence rates of CIN III and cervical cancer were 267/100,000 person-years among women who had never smoked, 183/100,000 person-years among exsmokers, and 476/100,000 person-years among current smokers. A multivariate model containing terms for age, marital status, and frequency of intoxication yielded a relative rate for current smokers compared with nonsmokers of 1.5 (95% confidence interval 1.0-2.2). Statistical trend tests for the number of cigarettes smoked per day (never, 1-14, and greater than or equal to 15 cigarettes), years of smoking (never, 1-9, and greater than or equal to 10 years), and age started smoking (less than 16, 16-18, 19-21, and greater than or equal to 22 years) all yielded significant results. These findings support the opinion that CIN III and cervical cancer are a smoking-related disease.