To compare the effect of organised pap-smear screening for cervical cancer with that of the spontaneous one on the incidence of invasive cervical cancer, we performed a case-control study within the catchment area of the Helsinki University Hospital (Helsinki, Finland). The study material consisted of 179 incident cases of invasive cervical cancer and 1,507 population controls. Data on lifetime pap smears before the year of the cancer diagnosis were collected using a self-administered questionnaire. The questionnaire information was obtained for 82% of the cases and 73% of the controls. The main outcome measure was relative risk of invasive cervical cancer among those with history of organised or spontaneous screening compared with risk among those with no history of screening for cervical cancer, measured as odds ratios (OR) with 95% confidence intervals (CI) and computed with logistic regression. Odds ratio of invasive cervical cancer among those who participated in the organised screening programme was 0.38 (CI 0.26-0.56) whereas any lifetime spontaneous pap smear had an OR value of 0.82 (CI 0. 53-1.26), in terms of unit risk for those not subjected to any screening and adjusted for age and the other type of the screening activity. Our results indicate that the substantial decrease in the incidence of and mortality due to cervical cancer in Finland is mainly due to the organised mass-screening.
Copyright 1999 Wiley-Liss, Inc.