International incidence rates of invasive cervical cancer after introduction of cytological screening

Abstract

Because Pap-smear screening can detect pre-invasive cervical cancer,such screening can markedly reduce the occurrence of invasive cancer.However, its impact in different populations is uncertain. This studycompares the changes in cervical cancer incidence at different ages after theintroduction of screening in different populations, and addresses the impactof organized and opportunistic smear taking. We identified 17 cancerregistries large enough and existing long enough to analyze screeningeffects. For each registry, we calculated the relative reduction inage-specific incidence rates and in incidence rates age-standardized to theworld population after the introduction of cytologic screening. In 11 of the17 populations, age-standardized incidence rates declined markedly from 27percent in Norway and to 77 percent in Finland. Age-specific declines wereconfined to women aged 30 to 70 years old with a nadir around ages 40 to 55.In six other populations, age-standardize d incidence rates declined lessthan 25 percent, an amount too small to provide unambiguous evidence of ascreening effect. In several populations, cytologic screening had a morepronounced effect than is generally recognized. Because age-specific declinesin cervical cancer incidence rates were strikingly similar in populationswith widely different screening practices, organized screening may not bemarkedly superior to opportunistic screening. The reduction in reportedcancer incidence because of screening is smaller in younger and older women.