Much ado about mammography variability

Assessing reader performance in radiology, an imperfect science: lessons from breast screening

The purpose of this article is to review the limitations associated with current methods of assessing reader accuracy in mammography screening programmes. Clinical audit is commonly used as a quality-assurance tool to monitor the performance of screen readers; however, a number of the metrics employed, such as recall rate as a surrogate for specificity, do not always accurately measure the intended clinical feature. Alternatively, standardized screening test sets, which benefit from ease of application, immediacy of results, and quicker assessment of quality improvement plans, suffer from experimental confounders, thus questioning the relevance of these laboratory-type screening test sets to clinical performance. Four key factors that impact on the external validity of screening test sets were identified: the nature and extent of scrutiny of one's action, the artificiality of the environment, the over-simplification of responses, and prevalence of abnormality. The impact of these factors on radiological and other contexts is discussed, and although it is important to acknowledge the benefit of standardized screening test sets, issues relating to the relevance of test sets to clinical activities remain. The degree of correlation between performance based on real-life clinical audit and performances at screen read test sets must be better understood and specific causal agents for any lack of correlation identified.

Diagnostic precision and accuracy in interpretation of specimens from cancer screening programs

Few areas in modern medicine provide a better example of evidence-based data than the anatomic pathologists' classification of fully developed malignancies. Beginning with the Papanicolaou (Pap) smear, morphologic tools also were applied to specimens obtained in cancer screening programs directed at large, asymptomatic patient populations. The Papanicolaou test was quickly responsible for a reduction in the incidence of invasive squamous cell carcinoma of the cervix, proving the concept that screening could interdict the development of advanced malignancy. Other screening programs followed the Papanicolaou test initiative, producing a revolutionary change in the specimens submitted to pathologists. Cancer screening generates specimens containing morphologic deviations from normal that are thought to put currently healthy patients at risk of future malignancy. However, translating morphologic findings in such samples into risk estimates raises a number of statistical and ethical problems. When diagnostic thresholds are set to favor specificity, unwanted false-negative results accrue. Conversely, aiming at sensitivity over specificity is associated with biologically false-positive results, which are likewise undesirable. Pathologists interpreting these specimens find themselves facing a screening paradox. These screening programs attempt to discover the very earliest changes of neoplastic transformation, but these same earliest changes are inherently the most difficult to identify with precision and accuracy. This paper discusses these challenges.

A Model-Based Comparison of Breast Cancer Screening Strategies: Mammograms and Clinical Breast Examinations

In screening for secondary prevention of breast cancer, clinical breast examination (CBE) combined with mammography may improve overall screening sensitivity compared with mammography alone. A systematic evaluation of the relative expenses and projected benefit of combining these two screening modalities is not presently available. We addressed this issue using a microsimulation model incorporating age-specific preclinical duration of the disease, age-specific sensitivities of the two modalities, age-specific incidence of the disease, screening strategy, and competing causes of mortality. We examined a total of 48 screening strategies, depending on the age range, the examination interval, and whether mammography or CBE is given at every one or two exam. Our results indicate that a biennial mammography can be cost-effective if coupled with annual CBE. For each screening interval and starting age, giving mammography every two exams and CBE at every exam has the lowest marginal cost per year of quality-adjusted life saved, whereas giving both at every exam has the highest. Comparing annual mammography and CBE to biennial mammography and annual CBE from 50 to 79, the total cost was reduced by 35%, whereas the marginal quality-adjusted life years only decreased by 12%. Similar reductions are observed for other starting ages. It is cost-effective to have a biennial mammography if coupled with an annual CBE. Annual mammography combined with CBE every 6 months will lead to a 41% increase in the quality-adjusted life years compared with annual mammography and CBE from 50 to 79, whereas the total cost increases by 30%.