NON-PROGRESSION OF CERVICAL INTRAEPITHELIAL NEOPLASIA ESTIMATED FROM POPULATION-SCREENING DATA

Non-progression and duration of preclinical neoplastic lesions of the cervix uteri were studied using screening data from a previously unscr eened population, Maribo County, Denmark (1966-82). To estimate regres sion rates, the incidence of clinical cancer before the screening prog ramme was related to the prevalence and incidence of preclinical lesio ns estimated from the detection rates of first smear and third and sub sequent smears respectively. Duration was estimated from the time lag between the cumulative incidence of preclinical lesions and the combin ed cumulative incidence of clinical cancer and the estimated 'incidenc e of regression'. Of all preclinical lesions in women aged 25-50, 24% progressed, 39% regressed and 38% remained. Even if we assume no onset of preclinical lesions above age 50, we estimated that 48% of the pre clinical lesions would not progress to clinical cancer in the women's lifetime. The estimated mean duration of preclinical lesions was 16 ye ars. In Maribo County during the 1970s, the positive rate (1.6%) was l ow compared with current rates in several countries. We conclude that the detection of non-progressive lesions was outweighed by the prevent ion of clinical cancer.