Risk of cervical cancer following negative smears in Maribo County, Denmark, 1966-1982.

In order to estimate the risk of developing cervical cancer among women who had originally had cytologically normal smears, information has been collected on all smears taken in Maribo County, Denmark, in the years 1966-1982, among women born between 1918 and 1952. A total of 27,811 women are included in the study, and cases of invasive cervical cancer developing in the study population have been identified from the local department of pathology and from the National Cancer Registry. The incidence of cervical cancer has been tabulated by number of previous negative smears and by time elapsed since last negative smear. Women with one previous negative smear have a zero risk of developing cervical cancer during the first year following the negative smear. The incidence among these women increases with length of time since the negative smear and reaches the same level as that of unscreened women during the fifth year of follow-up. Women with two to four previous negative smears also have a negligible risk of developing cervical cancer during the first two years following the last negative smear. The incidence among these women increases less over time than the incidence for women with one previous negative smear. No case of cervical cancer was observed among 7716 women with five or more previous negative smears. The study indicates that the five-year risk of developing cervical cancer is 48% lower in women with one previous negative smear than in an unselected population of unscreened women. The five-year risk for women with two previous negative smears is 62% lower than that for unscreened women.