Study of cervical cytopathology prevalence and natural history of cervical intraepithelial neoplasia in Taiwan

• Main Author: 嚴孟祿
• Other Authors: 林瑞雄
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/34023214618984722811

博士 === 國立臺灣大學 === 流行病學研究所 === 91 === Cervical cancer is the second most common malignancy for women in Taiwan, contributing to a quarter of all female cancer cases in the country. It remains one of the most pressing medical problems for Taiwanese women. The natural history of cervical cancer begins with a normal epithelium which progress through various stages of dysplasia─cervical intraepithelial neoplasia grade 1 (CIN 1), CIN 2, CIN 3─and, finally, to invasive cervical cancer (ICC). There is a long time interval for the progression to ICC, and consensus on the fact that regression occurs in CIN. The most important part of therapy is to detect and eradicate local CIN 3 lesions before the progression to ICC and metastasis can occur. The Papanicolaou (Pap) smear, a simple cytological screening test, has been used widely as the most effective screening tool for detecting precancerous cervical lesions (i.e. CIN 1, CIN 2, and CIN 3). However, the question remains: what is the most optimal screening interval for each woman? At stake is the considerable financial cost and cost-effectiveness of implementation. In order to examine this issue, the frequency of progression for the various stages of precancerous lesion must be known; in other words, the rate of progression for all the stages of dysplasia from normal to ICC (normal à CIN 1 à CIN 2 àCIN 3 à ICC) must be established. What is the rate of progression, regression, and/or stasis from one stage to another? What is the time interval in which these changes are detected? Thus, the two issues are critical to the prevention of cervical cancer on a public health level. This first part of this study was to analyze the prevalence of various cytological diagnoses in Taiwan, using the 1996 Taiwan cervical Pap smear database, which included approximately 900,000 cases. This national database encompassed all the Pap smear done for that year and included 10.66% of all women above the age of 15. Thus, the analyzed data was reliable and representative of the population in question. The results showed that in 1996, the frequency of ACUS (atypical cells of undetermined significance), CIN 1, CIN 2, CIN 3 and ICC was 0.74%, 0.46%, 0.18%, 0.28%, and 0.11%, respectively. This is the first ever set of such data and will be crucial in future comparisons and follow-up, as well as a reference for future public health policy formation. Analysis by geographical region (city/magistrate) was done, also with the thought of future use of such data as a reference for public health agencies. The second part of this study was an analysis of the rate of progression and/or regression for CIN. The case numbers for CIN 1 with follow-up of one year, two years, three years, and four years are 13197, 8464, 4887, and 2185, respectively. For CIN2 with follow-up of one year, two years, three years, and four years, the case numbers are 9113, 5723, 3387, and 1775, respectively. To date, this is the largest database for analysis of CIN progression/regression. Our results showed that the annual rates of CIN 1 progression to CIN 2 and CIN 3 after follow-up of one, two, three and four years are 3.31%, 2.42%, 1.49%, 0.82% and 2.62%, 2.47%, 2.15%, 0.96%, respectively. The annual rates of CIN 2 progression to CIN 3 are 2.51% for one-year follow-up, 1.85% for two-year follow-up, 1.74% for three-year follow-up, and 1.41% for four-year follow-up. Analyses based on age were also performed, with division into five age groups: 15-29 years, 30-39 years, 40-49 years, 50-59 years, and 60 years and above. The results show that the progression rates to CIN 3 from CIN 1 or normal are very similar for all groups 59 years and younger, and no difference in rate of progression was seen between different screening intervals. However, in the age group of 60 years and above, the rate was two to three times that of the younger age groups. These results hint at a need for more frequent screening for women aged 60 and above. Among other reasons, a factor which may explain these results could be the onset of menopause, the changes in hormonal milieu it brings and its effects on cervical epithelium. Further research is necessary to determine the cause of these initial results. Lastly, analyses of rate progression/regression of CIN were done based on infection status. The annual rate of progression for a normal (non-dysplastic) smear with infection to CIN 1 or CIN 2 is higher than one without infection. Rates of regression for CIN 1 smears with infection to normal is consistent year to year; however, for CIN 1 smears without infection, increasing annual rates of regression can be seen. Moreover, the progression to CIN 2 is more rapid for CIN 1 smears with infection than without infection. From these results, smears with infection show a more rapid progression than those without infection. In conclusion, a two- to three-fold increase in progression rates of increasing dysplasia in women 60 years and older suggest a need for a more frequent screening interval for older women. Decreasing annual rates of progression for increasing intervals of follow-up were seen, and increasing rates of progression (or decreasing rates of regression) were seen for smears with infection compared with smears without. The results from this largest database to date on cervical Pap smears are an important reference point for the formation of public health policy on cervical cancer screening and prevention in Taiwan.