How many cervical cancers are prevented by treatment of screen-detected disease in young women?

Others have argued that as many as a third of women treated for high-grade cervical intraepithelial neoplasia (CIN) would have developed cervical cancer in the absence of screening and treatment. Under various assumptions and using past data on CIN grade 3 (CIN3) registrations in England and Scotland, we estimate what cervical cancer rates would have been in the absence of screening. Data on registrations of cervical carcinoma in situ for England and Scotland were used to project the additional numbers of invasive cervical cancers that would have resulted had the carcinoma in situ not been treated. We compare the resulting cervical cancer rates (under different models) with rates recorded in Cancer Incidence in 5 Continents. In order for the projected rates in England and Scotland at ages 20-24 not to be exceptionally high compared to maximum recorded rates for each registry in Cancer Incidence in 5 Continents, the progression rate from CIN3 to invasive cancer in women aged 20-24 should not exceed 1% per year. Similar progression rates were reasonable for women aged 25-29. Under the previously accepted assumption of 4.33% progression per year, cervical cancer rates in women aged 20-29 in both England and Scotland would have been 2-5 times greater than any observed rate (other than one registry, based on just 4 cases). From this analysis, at most 1.5% of women treated (equivalent to 3% of CIN3 registrations) would have had cancer by age 25, whereas it is reasonable to assume that over half of them would have regressed by age 25. Copyright (c) 2008 Wiley-Liss, Inc.