Risk of cervical cancer subsequent to a positive screening cytology: follow-up study in Finland

Background. The purpose of the study was to estimate subsequent incidence of cervical cancer among women with positive cytology followed by negative histology. Methods. This was a longitudinal cohort study involving about 80,000 women with class II, III, IV or V cytology at the organized mass screening in Finland in 1971-1990. Follow-up through the Finnish Cancer Registry started from the fifth month following the initial screening and ended on December 31, 1995. Results. Standardized incidence ratios (SIR) of invasive cervical cancer varied from 2.2 (class II) to 19 (class V), and SIRs of preinvasive lesion varied from 3.0 (class II) to 20 (class V) compared to the risk among the total Finnish female population of same age and calendar period. The relative risk was greatest during first years of follow-up for both preinvasive and invasive cervical lesions, and it remained significantly high over 5 years of follow-up. For women with class II cytology there were peaks in relative risk in the years of subsequent rescreenings. Conclusion. Women with positive cytology have a high relative risk of cervical cancer even when excluding the cancers found at screening; the high relative risk is persistent for more than 5 years, and therefore these women should be kept under close surveillance and repeated smears should be taken with relatively short intervals.