Natural history of dysplasia of the uterine cervix

Background: A historical cohort of Toronto (Ontario, Canada) women whose Pa p smear histories were recorded at a major cytopathology laboratory provide d the opportunity to study progression and regression of cervical dysplasia in an era (1962-1980) during which cervical squamous lesions were managed conservatively. Methods: Actuarial and Cox's survival analyses were used to estimate the rates and relative risks of progression and regression of mil d (cervical intraepithelial neoplasia 1 [CIN1]) and moderate (CIN2) dysplas ias, In addition, more than 17 000 women with a history of Pap smears betwe en 1970 and 1980 inclusive and who were diagnosed as having mild, moderate, or severe dysplasia were linked to the Ontario Cancer Registry for the out come of any subsequent cervical cancers occurring through 1989. Results: Bo th mild and moderate dysplasias were more likely to regress than to progres s. The risk of progression from mild to severe dysplasia or worse was only 1% per year, but the risk of progression from moderate dysplasia was 16% wi thin 2 years and 25% within 5 years. Most of the excess risk of cervical ca ncer for severe and moderate dysplasias occurred within 2 years of the init ial dysplastic smear. After 2 Sears, in comparison with mild dysplasia, the relative risks for progression from severe or moderate dysplasia to cervic al cancer in situ or worse was 4.2 (95% confidence interval [CI] 3.0-5.7) a nd 2.5 (95% CI = 2.2-3.0), respectively. Conclusion: The risk of progressio n for moderate dysplasia was intermediate between the risks for mild and se vere dysplasia; thus, the moderate category may represent a clinically usef ul distinction. The majority of untreated mild dysplasias were recorded as regressing to yield a normal smear within 2 years.