Background: Prospective cohort studies to determine cofactors with oncogenic HPV-infections for cervical cancer are very rare from developing countries and such data are limited to the few screening trials. Large screening trials provide such data as a by product. Some of the cases are prevented by screening and do not surface as invasive cancers at all. Also, pre-invasive lesions are detected almost entirely by screening. Screening causes selection bias if attendance in or effectiveness of screening is correlated with the risk factors. The aim of this study was to quantify the influence of screening on risk factors for cervical cancer. Materials and Methods: Our material stems from a rural cohort of 80,000 women subjected to a randomised screening trial. The effect of screening on the incidence of cervix cancer was estimated with reference to socio-demographic and reproductive risk factors of cervical cancer. We compared these risks with the incidence of cancer in the randomised control population by the same determinants of risk. Results: The results in the screening arm compared to the control arm showed that the women of low SES and young age were benefitting more than those of high SES and old age. The relative risk by age (30-39 vs 50-59) was 0.33 in the control arm and 0.24 in the screening arm. The relative risk by education (not educated vs educated) was 2.8 in the control arm and 1.8 in the screening arm. The previously married women did not benefit (incidence 113 and 115 per 100,000 women years in control vs screening arms) whereas the effect was substantial in those married (86 vs 54). Conclusions: The results in controls were consistent with the general evidence, but results in attenders and nonattenders of the screening arm showed that screening itself and self-selection in attendance and effectiveness can influence the effect estimates of risk factors. The effect of cervical cancer screening programmes on the estimates of incidence of cervical cancer causes bias in the studies on etiology and, therefore, they should be interpreted with caution.
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机译：背景：前瞻性队列研究，以确定颈癌癌的癌症HPV感染的辅助型患者非常罕见，从发展中国家非常罕见，这些数据仅限于少数筛选试验。大型筛选试验提供了备份产品的数据。通过筛选和根本不作为侵入性癌症来预防一些病例。此外，几乎完全通过筛选来检测预侵入性病变。如果筛选的出勤或有效性与风险因素相关，筛选会导致选择偏差。本研究的目的是量化筛查对宫颈癌危险因素的影响。材料和方法：我们的材料源于80,000名妇女的农村队列，经过随机筛查试验。据据鉴于宫颈癌的社会人口统计和生殖危险因素，估计筛查对子宫颈癌发生率的影响。通过相同的风险决定因素将这些风险与随机对照人群中的癌症发生率进行了比较。结果：筛查臂与控制手臂相比的结果表明，低血糖和年轻时的女性受益于高年龄和晚年的妇女。对控制臂的相对风险（30-39 Vs 50-59）为0.33，筛选臂中的0.24。受教育（未经教育的VS受过教育）的相对风险在控制臂中为2.8，筛选臂中1.8。以前已婚的妇女没有受益（每10万名女性在控制VS筛查武器的情况下113和115岁），而效果在已婚的那些（86 VS 54）中是大幅的。结论：对照的结果与一般证据一致，但筛选手臂的出席人员和非特性人员的结果表明，筛查本身和出勤和有效性的自我选择会影响风险因素的效果估计。宫颈癌筛查计划对宫颈癌发生率估计的影响导致病因研究中的偏见，因此，应谨慎解释。
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