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 for these precursor lesions affect the benefit of screening. These criteria may be difficult to study, but they are likely to be reflected in reported incidence of in situ cancer in small areas of Sweden.
Purpose: Our purpose was to test the hypothesis that the benefit of screening can be predicted by histopathologic criteria as reflected in the reported incidence of cancer in situ.
Methods: Incidence data were from the Swedish National Cancer Registry. Regression models showing the relationship between in situ and invasive cancer were formulated and estimated. Each county (total, 24) was a unit of measurement, and adjustment was made for the incidence of invasive cancer before screening.
Results: During population-based screening in Sweden, the incidence of cancer in situ varied about fourfold among the 24 counties, which indicates that the criteria used to diagnose cancer in situ differed markedly. No statistically significant (P < .05) associations were found between the incidence of cancer in situ in 1965, 1970, or 1975 and the reduction in invasive cancer 5, 10, or 15 years later. According to the best-fitting model, detection of 100 extra cases of cancer in situ per 100,000 women per year in 1975 resulted in a reduction of 1.0 (95% confidence interval [CI] = -1.6-3.7) cases of invasive cancer 10 years later. The corresponding best model estimate implied a reduction of 4.6 cases (95% CI = 1.5-7.7) in a model restricted to cancer in situ in patients aged 20-50 years (when organized screening took place), invasive cancer in patients aged 30-60 years, and cancer in situ measured in 1970.
Conclusions: The absent, or at most weak, association between detection of cancer in situ and subsequent reduction in invasive cancer indicates that relaxed histopathologic criteria for cancer in situ may result in extensive, unnecessary treatment of lesions that would regress spontaneously.
Implication: Further studies are urgently needed to enable identification of neoplasms likely to progress to invasive, fatal disease.