Efficacy of National Cervical Cancer Screening Program in Taiwan

Cervical cancer is the second leading female cancer in the world. The long period of pre-cancerous detectable stage and the availability of a valid simple test with its non-invasive property make cervical cancer ideal for screening. Organized screening program in developed countries has been well documented to effectively reduce the incidence and mortality of cervical cancer, while opportunistic screening may also reduce cervical cancer morbidity and mortality with a lesser effect. Nation-wide screening program in Taiwan has been launched since 1995 to reimburse annual Pap smear to women aged more than 30 years old. The efficacy of the screening program in Taiwan was comprehensively investigated in this study using the long-term continuous data registered in the cervical cancer screening registry. The analysis of efficacy was assessed at population and individual levels, respectively. This study utilized several national registries to evaluate the cervical cancer screening efficacy, including cervical cancer screening registry, cervical and vaginal biopsy registry, household registry, death certificate registry, cancer registry, and catastrophic illness registry with the permission by the Bureau of Health Promotion, Department of Health, Executive Yuan, Taiwan. The secular trend of age- and calendar year-specific incidence and mortality of cervical cancer was assessed by Poisson regression analysis including calendar years and age groups in the models. Two cohort studies were conducted to assess the efficacy of cervical cancer screening at the individual level using computerized linkage to obtain information of screening history, the first abnormality detected by screening, follow-up attendance of Pap smear and biopsy examinations, date of cervical cancer diagnosis, and date at death. The associations with cervical cancer risk were assessed for screening and follow-up attendance by Cox’s proportional hazards models, and the cumulative incidences and mortality of cervical cancer were estimated by Nelson-Aalen method. The triennial screening participation in Taiwan increased from less than 10% to 51% from 1995 to 2007. Despite of the screening participation rate was not high, there was a 48% and 49% reduction in invasive cancer incidence and mortality, respectively. Compared with women who never attended cervical cancer screening from 1995 to 1999, women who attended cervical cancer screening once, twice, and three or more times had a 37%, 52%, and 60% reduction in invasive cervical cancer incidence, respectively; and a 58%, 70%, and 76% reduction in cervical cancer mortality, respectively, from 2001 to 2006. The risks of developing invasive cancer among women attended screening in recent years found to be normal were less than those not attended recently. However, if abnormal lesions have been found, women were not followed annually have higher risk, and there was no difference to detect abnormal lesion in the early or later period. The Pap smear screening also significantly reduced the incidence and mortality of invasive adenocarcinoma with a smaller reduction. Women first detected with atypical squamous cells, atypical glandular cells, or low-grade squamous intraepithelial lesions had at least 20% reduction in cervical cancer risk if they attended screening at two or more years before the detection, and at least 35% and 60% reduction of carcinoma in situ and invasive cervical cancer if they attended screening within 2 years before the detection compared with women who never attended screening. The attendance of follow-up examination after the first detection of cytological abnormality significantly reduced 12% to 48% of HSIL, 41% to 49% of carcinoma in situ, and 49% to 77% of invasive cervical cancer. In comparison with atypical squamous cells and low-grade squamous intraepithelial lesions, atypical glandular cells had the highest risk of developing clinically significant lesion. The success of reducing disease burden of cervical cancer through the implementation of a nationwide screening program was verified by the decreasing secular trend of cervical cancer incidence and mortality in women population, and by the reduction in risk of developing end-stage cervical diseases through the cohort study on 4.7 million women in Taiwan. Continuing to actively invite women not attended screening in recent three years was recommended. Women detected to be affected with low-grade abnormalities by screening need to be monitored carefully. It is suggested that women with atypical glandular cells should be included in the intensive positivity follow-up system in the screening program.