INTERNATIONAL INCIDENCE RATES OF INVASIVE CERVICAL-CANCER AFTER INTRODUCTION OF CYTOLOGICAL SCREENING

Because Pap-smear screening can detect pre-invasive cervical cancer, s uch screening can markedly reduce the occurrence of invasive cancer. H owever, its impact in different populations is uncertain. This study c ompares the changes in cervical cancer incidence at different ages aft er the introduction of screening in different populations, and address es the impact of organized and opportunistic smear taking. We identifi ed 17 cancer registries large enough and existing long enough to analy ze screening effects. For each registry, we calculated the relative re duction in age-specific incidence rates and in incidence rates age-sta ndardized to the world population after the introduction of cytologic screening. In II of the 17 populations, age-standardized incidence rat es declined markedly from 27 percent in Norway and to 77 percent in Fi nland. Age-specific declines were confined to women aged 30 to 70 year s old with a nadir around ages 40 to 55. In six other populations, age -standardized incidence rates declined less than 25 percent, an amount too small to provide unambiguous evidence of a screening effect. In s everal populations, cytologic screening had a more pronounced effect t han is generally recognized Because age-specific declines in cervical cancer incidence rates were strikingly similar in populations with wid ely different screening practices, organized screening may not be mark edly superior to opportunistic screening. The reduction in reported ca ncer incidence because of screening is smaller in younger and older wo men.