Background: The accuracy of screening for anal cancer precursors relative to screening for cervical cancer precursors has not been systematically examined. The aim of the current meta-analysis was to compare the relative accuracy of anal cytology to cervical cytology in discriminating between histopathologic high grade and lesser grades of dysplasia when the reference standard biopsy is obtained using colposcope magnification.
Methods and findings: The outcome metric of discrimination was the receiver operating characteristic (ROC) curve area. Random effects meta-analysis of eligible studies was performed with examination of sources of heterogeneity that included QUADAS criteria and selected covariates, in meta-regression models. Thirty three cervical and eleven anal screening studies were found to be eligible. The primary meta-analytic comparison suggested that anal cytologic screening is somewhat less discriminating than cervical cytologic screening (ROC area [95% confidence interval (C.I.)]: 0.834 [0.809-0.859] vs. 0.700 [0.664-0.735] for cervical and anal screening, respectively). This finding was robust when examined in meta-regression models of covariates differentially distributed by screening setting (anal, cervical).
Conclusions: Anal cytologic screening is somewhat less discriminating than cervical cytologic screening. Heterogeneity of estimates within each screening setting suggests that other factors influence estimates of screening accuracy. Among these are sampling and interpretation errors involving both cytology and biopsy as well as operator skill and experience.