Incidence of cervical cancer following negative smear. A cohort study from Maribo County, Denmark.

In order to estimate the risk of developing cervical cancer among women who originally had cytologically normal Papanicolaou (Pap) smears, information has been collected on all Pap smears taken in Maribo County, Denmark in 1966-1982 among women born 1918-1952. A total of 27,811 women are included in the study, and cases of invasive cervical cancer developed in the study population have been identified from the local department of pathology and from the Danish 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 level of unscreened women during the fifth year of follow-up. Women with 2-4 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 cases of cervical cancer were observed among 7,716 women with 5+ previous negative smears. The study indicates that the 5-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 5-year risk for women with 2-4 previous negative smears is 69% lower than that for unscreened women.