CIN 2/3 and cervical cancer in an organised screening programme after an unsatisfactory or a normal Pap smear: a seven-year prospective study of the Norwegian population-based screening programme

OBJECTIVES: To estimate the risk of cervical intraepithelial neoplasia (CIN) 2/3 and invasive cervical cancer (ICC) in an organised screening programme after an unsatisfactory or a normal Pap smear. SETTING: A seven-year prospective cohort study of the Norwegian population-based co-ordinated screening programme based on the actual diagnostic and screening procedures performed. Observations of 526,661 women with a normal index Pap smear and 21,405 women with an unsatisfactory index Pap smear were made during 3.26 million women-years. METHODS: The risk of being diagnosed with CIN 2/3 or ICC was calculated by logistic regression for the first two years of follow-up. The hazard of being diagnosed with CIN 2/3 or ICC for the women who were not diagnosed during the two first years was estimated by non-parametrical survival regression. RESULTS: After two years of follow-up, 0.2% of the women were diagnosed with CIN 2/3 and 0.01% with ICC after a normal Pap smear. An unsatisfactory Pap smear indicated a 1.6-4.0 times higher risk of harbouring a CIN 2/3 or ICC compared to women with a normal Pap smear. No increased risk of ICC was found during long-term follow-up for the 70% of the women with an unsatisfactory Pap smear who were returned to ordinary screening. Prior series of low-grade Pap smears followed by a normal Pap were associated with an increased risk of CIN 2/3 and ICC. CONCLUSIONS: An unsatisfactory Pap smear indicates a risk of harbouring CIN II/III or ICC. Repeated Pap smears are adequate as a follow-up of an unsatisfactory Pap smear. Women with repeated series of equivocal/LSIL Pap smears followed by a normal Pap should be considered at high risk.