TREATMENT OF PREINVASIVE CONDITIONS DURING OPPORTUNISTIC SCREENING AND ITS EFFECTIVENESS ON CERVICAL-CANCER INCIDENCE IN ONE NORWEGIAN COUNTY

Norway had until recently no organized screening programme for cervica l cancer, but opportunistic screening was common. This study focuses o n the effectiveness of treatment of pre-malignant cervical conditions (CIN III) on cervical-cancer incidence in the county of Sor-Trondelag in Norway, prior to the introduction of organized mass screening. The study is based on cervical-cancer incidence rates during the years 196 5-92 and treatment data for CIN III. The expected number of cervical-c ancer cases prevented due to early intervention was expressed in a reg ression model with 2 unknown parameters: the probability, p, of cancer development in case of CIN III, and the time lag, t, between treatmen t and when clinical cancer would otherwise have been diagnosed. The es timated probability that a patient treated for CIN III would have deve loped cervical cancer if not treated was found to be approximately 20% , and the mean time delay was around 16 years. In the last period of s tudy (1988-92), the incidence was reduced by nearly 40% of what would have been expected without early intervention. Based on equal treatmen t rates as in 1990, parameter estimates were used to predict future in cidence reduction. Maximum effectiveness will be achieved around the y ear 2005, with a nearly 70% reduction. Opportunistic screening and tre atment of CIN III seems to have had considerable influence on cervical -cancer incidence. The costs, however, are substantial over-treatment, since our results indicate that 4 of 5 women treated for CIN III woul d not progress into the invasive state. (C) 1997 Wiley-Liss, Inc.