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Background. Cytologic screening can reduce mortality from cervical cancer by detection and removal of premalignant lesions. Conceivably, mortality is further reduced because more women with invasive disease are diagnosed at an earlier, curable stage. This hypothesis can be assessed in Sweden, where population-based screening programs were introduced successively over about a decade starting in 1964. Methods. Record linkages permitted complete follow-up through 1986 of all 17,377 patients with invasive cervical cancer diagnosed in Sweden from 1960 through 1984. We analyzed relative survival rates that describe the survival of patients after elimination of the effects of causes of death other than cancer of the cervix. Results. Prognosis improved substantially in patients younger than age 50 years at diagnosis; from 1960-1964 to 1980-1984, the 5-year relative survival rate increased from 69.8% to 88.8% at age 20-29 years, from 71.7% to 85.5% at age 30-39 years, and from 68.6% to 77.9% at age 40-49 years. The excess mortality was thus reduced by more than half in patients diagnosed when younger than 40 years. In contrast, only slight or no improvement was noted in those diagnosed at older ages when screening was less extensive. In all time periods, a strong association was found between older age at diagnosis and poorer prognosis. Conclusion. Although alternative explanations for our findings must be seriously considered, the most obvious interpretation is that cytologic screening reduces mortality from cervical cancer by earlier diagnosis of invasive disease.

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