Incidence of cervical intraepithelial neoplasia grade III, and cancer of the cervix uteri following a negative Pap-smear in an opportunistic screening

Background. To investigate the influence of screening history on the diagnosis of cervical intraepithelial neoplasia grade three (CIN III) and cervical cancer in an opportunistic screening program. Design. Follow-up study of women with a negative Pap-smear at entry. Materials. Records from 41212 women pertaining to cervical specimens in the Pathology Registry of the University Hospital in Tromso. Results. During the 175,673 person-years (pyr) of observation, 396 incident cases (379 of CIN III and 17 of cervical cancer) were identified. The age specific incidence rate was highest among women who were 25 to 29 years old (396 per 100,000 pyr). A Poisson multiple regression model yielded statistically significant positive associations between time since last negative Pap-smear and the incidence of CIN III and cervical cancer. Most CIN III cases were diagnosed subsequently to a CIN I or CIN II diagnosis. Including only women with a CIN III diagnosis directly after a negative Pap-smear in the analyses revealed that women with less than two years (Relative rate (RR)=1.0; 95% CI 0.7-1.4) and three years (RR=0.8; 95% CI 0.4-1.4) since their last negative Pap-smear were not at an increased risk compared with the women with a negative Pap-smear within the last year. Women with three or more years since their last negative Pap-smear were at an increased risk (RR=1.3; 95% CI 0.6-3.2) for CIN III. No meaningful association between number of negative specimens and the risk of CIN III was revealed. Conclusion. This study indicates that time since last negative Pap-smear does, while number of such does not, influence the risk of CIN III and cervical cancer in an opportunistic screening.