The past 15 years have seen a near universal switch from film-screen mammography to digital mammography as the standard diagnostic tool in breast cancer screening. The digital version offers vastly improved contrast, making it far easier to detect the types of calcifications that are key to diagnosing ductal carcinoma in situ (DCIS), a preinvasive form of breast cancer that the American Cancer Society estimated accounted for about 15% of newly diagnosed female breast cancers in 2020. But physicians wondered: Is this more-sensitive mammography increasing the detection rate of DCIS? And has it affected the rate at which DCIS is upgraded to invasive cancer?
In the April 2021 issue of the American Journal of Roentgenology1, a team of physician-researchers at the University of Michigan and Emory University explored these questions and found that while digital mammography has led to a significant increase in both DCIS and high-grade DCIS detection, this heightened detection has not led to any major increases in upgrade rates.
“It was not a surprise to learn that [digital mammography] was not associated with a higher upgrade rate to invasive cancer,” stated Colleen H. Neal, MD, of the University of Michigan in Ann Arbor, and lead author of the study. “If anything, I was expecting that [digital mammography] might be associated with a lower upgrade rate to invasive cancer through the detection of more low- and intermediate-grade DCIS.”
To reach this conclusion, the researchers took a retroactive look at department records from the University of Michigan’s National Cancer Institute–designated cancer center. The review included mammograms evaluated from January 1, 2001 to December 31, 2014. During that time, 459,945 mammograms were captured—232,532 on film and 227,413 digitally, providing an intentionally even split in imaging approach.
Ultimately, 484 cases of DCIS were detected in the study pool and, of those, 33% were diagnosed through film-screen mammography and 67% through digital mammography; a 2-fold increase in detection that led the researchers to conclude that the digital tool does in fact detect DCIS at a higher rate. Only patients whose DCIS diagnosis was specifically tied to the mammographic detection of calcifications were included in the study conducted by Dr Neal and colleagues — excluding, for example, DCIS diagnoses originating from other forms of detection, such as excisional biopsy, and patients who had experienced ipsilateral breast cancer within the prior 2 years.
The researchers also evaluated the upgrade rate from DCIS to invasive breast cancer between film-screen mammography and digital mammography. In both cases, the upgrade rate was 10%, showing that cancer grading remained stable regardless of the nature of the mammogram used in initial detection.