Existing data sources for clinical epidemiology: the Danish Quality Database of Mammography Screening

The Danish Quality Database of Mammography Screening (DKMS) was established in 2007, when screening was implemented on a nationwide basis and offered biennially to all Danish women aged 50-69 years. The primary aims of the database are to monitor and evaluate the quality of the screening program and - after years of follow-up - to evaluate the effect of nationwide screening on breast cancer-specific mortality. Here, we describe the database and present results for quality assurance from the first round of national screening. The steering committee for the DKMS defined eleven organizational and clinical quality indicators and standards to monitor the Danish breast cancer screening program. We calculated the relevant proportions and ratios with 95% confidence intervals for each quality indicator. All indicators were assessed on a national and regional level. Of 670,039 women invited for mammography, 518,823 (77.4%) participated. Seventy-one percent of the women received the result of their mammography examination within 10 days of screening, and 3% of the participants were recalled for further investigation. Among all detected cancers, 86% were invasive cancers, and the proportion of women with node negative cancer was 67%. There were 36% women with small cancers, and the ratio of surgery for benign lesions to malignant lesions was 1:6.3. A total of 80% of women with invasive cancers were treated with breast conserving therapy. Screening interval and interval cancers were not relevant in the first round, and data regarding radiation dose were not available at the time of evaluation. Overall, the quality indicators showed satisfactory quality in the first round of national breast cancer screening in Denmark. The DKMS is a potentially valuable tool for improving quality and conducting research in the field of breast cancer screening.