DETECTION OF PREINVASIVE CANCER OF THE CERVIX AND THE SUBSEQUENT REDUCTION IN INVASIVE CANCER

Background: Cytologic screening and follow-up can reduce the incidence of cervical cancer by detection and removal of precursor lesions. It is unknown, however, whether differences in histopathologic criteria f or these precursor lesions affect the benefit of screening. These crit eria may be difficult to study, but they are likely to be reflected in reported incidence of in situ cancer in small areas of Sweden. Purpos e: Our purpose was to test the hypothesis that the benefit of screenin g can be predicted by histopathologic criteria as reflected in the rep orted incidence of cancer in situ. Methods: Incidence data were from t he Swedish National Cancer Registry. Regression models showing the rel ationship between in situ and invasive cancer were formulated and esti mated. Each county (total, 24) was a unit of measurement, and adjustme nt was made for the incidence of invasive cancer before screening. Res ults: During population-based screening in Sweden, the incidence of ca ncer in situ varied about fourfold among the 24 counties, which indica tes that the criteria used to diagnose cancer in situ differed markedl y. No statistically significant (P<.05) associations were found betwee n the incidence of cancer in situ in 1965, 1970, or 1975 and the reduc tion in invasive cancer 5, 10, or 15 years later. According to the bes t-fitting model, detection of 100 extra cases of cancer in situ per 10 0000 women per year in 1975 resulted in a reduction of 1.0 (95% confid ence interval [CI] = -1.6-3.7) cases of invasive cancer 10 years later . The corresponding best model estimate implied a reduction of 4.6 cas es (95% CI = 1.5-7.7) in a model restricted to cancer in situ in patie nts aged 20-50 years (when organized screening took place), invasive c ancer in patients aged 30-60 years, and cancer in situ measured in 197 0. Conclusions: The absent, or at most weak, association between detec tion of cancer in situ and subsequent reduction in invasive cancer ind icates that relaxed histopathologic criteria for cancer in situ may re sult in extensive, unnecessary treatment of lesions that would regress spontaneously. Implication: Further studies are urgently needed to en able identification of neoplasms likely to progress to invasive, fatal disease.