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QUESTION: In adult women at average risk for cervical cancer, what is the accuracy of the conventional Papanicolaou (Pap) test and of new technologies (thin layer cytology, computer rescreening, and algorithm based decision making) in detecting cervical cancer and cervical intraepithelial neoplasia?
Studies were identified by searching Medline, CancerLIT, HealthSTAR, CINAHL, EMBASE/Excerpta Medica, and EconLIT; scanning recent issues of selected journals; and contacting manufacturers of automated cytologic devices and relevant professional societies.
Studies were selected if cervical cytology was evaluated as a screening test, the reference standard was histology or colposcopy, and sensitivity and specificity (or relative true positive and false positive rates) could be calculated. Cytology was an acceptable reference standard if the studies also included an independent panel of cytology specialists to arrive at a consensus diagnosis and a 2 arm prospective study design was used. The cost analysis considered the cost of all medical services provided for screening, diagnosis, and treatment.
2 reviewers independently extracted data, permitting calculation of sensitivity, specificity, and prevalence. Definitions of cytologic abnormality were extracted and defined by 1 of 3 thresholds: atypical squamous cells of uncertain significance (ASCUS), low grade squamous intraepithelial lesions (LSIL), and high grade squamous intraepithelial lesions (HSIL). Test characteristics were compared for cytologic and histological results at 4 thresholds: ASCUS/cervical intraepithelial neoplasia (CIN) 1, LSIL/CIN1, LSIL/CIN2-3, and HSIL/CIN2-3.
86 studies met inclusion criteria. The evidence was insufficient to assess the accuracy of the newer technologies. 84 studies were included in a meta-analysis of conventional Pap test accuracy, but only 3 studies controlled for severe biases of disease prevalence and verification. These 3 studies showed conventional Pap test sensitivities of 56%, 53%, and 29% and specificities of 98%, 100%, and 97%. The cost effectiveness of conventional Pap screening every 3 years compared with no Pap screening was US$4079 per life year saved. The addition of improved screening technology every 3 years had an incremental cost of US$22 010 per life year saved.
Implementation of newer technologies improves the sensitivity of primary cervical screening compared with the conventional Papanicolaou test but at a substantial increase in cost per life year saved. Current evidence is not sufficient to justify routine implementation of newer technologies.
The Pap test has been successful in reducing morbidity and mortality from cervical cancer in countries with organised screening programmes. Worldwide, however, cervical cancer is the fourth leading cause of death from cancer among women. 1 Concerns about the screening accuracy of the Pap test have led to the development of new technologies (liquid based cytology, computer assisted screening, and human papillomavirus testing).
In the US, 60% of deaths caused by cervical cancer has been attributed to lack of screening or inadequate follow up of abnormal results. 2 In developing countries, the primary obstacles to successful screening are cost, availability of trained personnel, and acceptability of pelvic examinations. In this context, improving screening accuracy is less important than broadening screening coverage, lowering costs, reducing the need for highly trained personnel, and improving follow up.
McCrory et al did an exhaustive review on the accuracy of cervical cytology and new technologies. Unfortunately, because of the lack of high quality research, they could not meet their objectives. Although 86 studies met their inclusion criteria, only 2 addressed new technologies. Only 3 of 84 studies on cervical cytology took sufficient precautions to avoid bias. The sensitivity for conventional cytology in these studies was relatively low, but it performed best in the detection of high grade dysplasia, which is most likely to progress to cancer if left untreated. 3
Furthermore, the estimated cost effectiveness of conventional cytology every 3 years compared with no screening was substantially better than the marginal cost effectiveness of adding on new technologies. Rigorous research is needed to evaluate automated primary screening, which could reduce the need for cytotechnologists, and to evaluate the use of technologies that might replace cervical cytology or permit longer screening intervals. Conserved resources could then be allocated to broaden screening coverage and improve follow up.
Source of funding: Agency for Health Care Policy and Research.
For correspondence: Director, Center for Practice and Technology Assessment, Agency for Health Care Policy and Research, 6010 Executive Boulevard, Suite 300, Rockville, MD 20852, USA. Fax +1 919 286 5601.