Page 41 - Screening for Cervical Cancer: Systematic Evidence Review

Chapter III. Results

the study populations. Relative comparisons of the effectiveness of the screening systems and of

the potential impact of screening interval cannot be made across studies.

With these caveats, we describe in greater detail selected studies of incidence of

histologic or cytologic abnormalities among previously screened women, prevalence within

screening programs, and the influence of interval and prior screening history on probability of

detecting abnormalities.

Incidence and Age

Each of the studies reporting incidence of CIN and more serious lesions constructed their

cohort by requiring a normal Pap test as the earliest reference point. Computerized record-

keeping systems from a single cytology laboratory 34,35 assure relative consistency of quality of

examination of the baseline and subsequent Pap tests; in relatively stable populations, they also

allow exclusion of women with prior documentation of abnormal cytology. Sawaya and

colleagues prospectively gathered data assuring that baseline cytology for individuals entering

the study was reported as normal; however, this does not exclude the possibility that participants

may have had a more remote history of dysplasia evaluation or treatment. 26,36,44 In the reports

based on the National Breast and Cervical Cancer Early Detection Program, laboratory facilities

across the United States processed Pap tests; 26,36 in the Heart and Estrogen/progestin

Replacement Study (HERS) study, a single commercial laboratory (Empire Pathology Medical

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Group, Garden Grove, CA) processed tests.

Despite these distinctions and different groupings of age in the analysis of data, estimates

of incidence of high-grade lesions are compatible across the studies of incidence: 1.0 per 1,000

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women 41 years of age and older, screened at an interval of approximately 1 year; 1.2 per

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