When large, population-based breast cancer screening programs switch from screen-film mammography to digital mammography, the detection of life-threatening cancer is improved and the detection of clinically insignificant disease is not significantly increased.

The research team, from the Netherlands, studied the performance of digital mammography in three screening regions before the country had a nationwide transition to digital mammography. Digital mammograms were compared with screen-film mammograms in screening mammography that occurred between 2003 and 2007. Of the almost 2,000,000 mammograms studied, 18,895 cases were indicated for recall, and 6,410 women received diagnoses of breast cancer.

Since digital mammography has higher sensitivity at detecting breast cancer, concerns had been raised about its introduction leading to increased diagnosis of clinically unimportant cancers, which are those that, if left untreated, would never have surfaced clinically in the person’s lifetime. As expected, digital mammography had a higher initial sensitivity for detecting cancer, with a detection rate per 1,000 of 6.8, compared with 5.6 for screen-film mammography.

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This study found an increased incidence of ductal carcinoma in situ (DCIS), which is a precursor for invasive breast cancer, in the years after the introduction of population-based screening with digital mammography. While low-grade DCIS may develop over more than three decades, high-grade DCIS is associated with far more rapid cancer invasion. For high-grade DCIS, the detection rate with digital mammography was 58.5%, compared with 50.5% for screen film mammography.

“More DCIS and invasive cancers are detected with the use of digital mammography in breast cancer screening compared to screen film mammography,” said Adriana M.J. Bluekens, MD, from the National Expert and Training Centre for Breast Cancer Screening in Nijmegen and St. Elisabeth Hospital in Tilburg, both in the Netherlands. “In the mix of low- to high-grade DCIS lesions, there is no shift to the detection of low-grade lesions in digital screening. Instead of this, we noticed a larger amount of high-grade lesions, which are regarded as precursors of high-grade invasive tumors.”

With digital mammography, the initial recall rate of 4.4% was higher than that for screen-film mammography (2.6%). Notably, transitioning to digital mammography did not lead to a disproportionate increase in low-grade DCIS lesions, which are associated with possible overdiagnosis.

The study provides further evidence of the benefits of using digital mammography in population-based breast cancer screening programs. Bluekens noted, “The follow-up period of the different digital screening programs is not sufficiently long enough to analyze mortality effect separately from that of screen-film mammography. However, surrogate parameters, such as stage distribution and tumor characteristics of digital mammography-detected cancers, do indicate the continuation of mortality decrease with the transformation of screen-film to digital mammography in screening programs.”

The Dutch screening program focuses on balancing rates of detection, recall, and false-positives. US screening programs focus more on a high detection rate, and so numbers are likely to be different.

This research by Bluekens and colleagues was published in Radiology (2012; doi:10.1148/radiol.12111461).