Risk of cervical cancer after a negative Pap smear

To evaluate whether five years is an appropriate screening interval for cervical cancer for the improvement of public health.

Finland.

45,572 women with a cytological class I smear attending the mass screening programme organised every five years in Finland during 1971 to 1976 and followed up until the end of 1994. The data from the Nationwide Mass Screening Registry were linked to the Finnish Cancer Registry. Standardised incidence ratios of preinvasive and invasive cervical cancer with 95% confidence intervals (CI) were estimated, with rates for the total Finnish population as reference.

The standardised incidence ratio estimates were low initially after screening and then gradually increased up to the time of the next smear five years later. This pattern was repeated after each screening. The risk was persistently low for invasive cervical cancer even after 10 years of follow up, whereas the low risk for preinvasive lesions was of a shorter duration. The low risk associated with a negative smear became even lower with advancing age.

Women who attend organised screening programmes and have a negative smear have a low risk of cervical cancer for over 10 years. Also, the relative risk of a preinvasive lesion after an initial negative smear is decreased for more than five years. Therefore, the five year screening interval in Finland is appropriate and effective in reducing the risk of invasive cervical cancer.