Breast cancer screening, diagnostic accuracy and health care policies

The criteria for an effective screening program are well established: the disease should pose a substantial burden, it should have an understood latency period, and there should be acceptable screening tests and therapeutic interventions available. Few would dispute the appropriateness of breast cancer screening (at least for women aged 50-69 years). In most scientific forums, the discussion about breast cancer screening has progressed beyond "whether" to "how." In this issue (see page 195) Théberge and colleagues seek to maximize the operating characteristics of screening mammography by investigating whether the sensitivity and specificity of the test are associated with the volume of mammograms read by individual radiologists or the volume performed by individual health care facilities.1 They conclude that radiologists who work in larger facilities and who read more screening mammograms are more likely to have higher breast cancer detection rates and lower false-positive rates. A radiologist's ability to interpret mammograms is critical for the efficacy of screening mammography programs. Previous studies have shown substantial variation in interpretation and reading accuracy among radiologists. Some studies have suggested that sensitivity and specificity are associated with the volume of mammograms read by a radiologist. Others have shown that this factor may not be important.8-14 The study by Théberge and colleagues in this issue1 shows that the operating characteristics of screening mammography improve with the increasing size of the facility and volume of mammograms read by individual radiologists. This finding is based on a comparative analysis of data of facility and radiologist characteristics associated with 1709 cases of screening-detected breast cancer and 3159 cases of false-positive readings in a 10% random sample of women without screening-detected breast cancer (n = 30 560) obtained from the population-based Quebec Breast Cancer Screening Program. The authors report that the adjusted breast cancer detection rate ratio for facilities performing 4000 or more screenings per year, compared with the rate ratio for facilities performing fewer than 2000, was 1.28 (95% confidence interval [CI] 1.07-1.52). They also report that the adjusted false-positive rate ratio for radiologists who read 1500 or more screening mammograms a year, compared with radiologists who read fewer than 250, was 0.53 (95% CI 0.35-0.79). These results should be interpreted ca