Radiology: Even with digital mammo, missed cancers plague breast imagers

Mammography computer-aided detection (CAD) Source: Definiens

The transition to digital mammography has not solved the challenge of missed cancers in screening mammography. The percentage of missed interval and screen-detected cancers was comparable in film and digital programs, according to a study published online June 14 in Radiology.

Previous research has indicated a higher rate of cancer detection in digital mammography compared with film-based mammography, which might suggest a decline in the missed cancer rate with the transition to digital mammography.

Solveig R. Hoff, MD, from the department of radiology at Aalesund Hospital in Aalesund, Norway, and colleagues devised a retrospective analysis to test the hypothesis and compare the percentages of mammographic features of missed cancers on film and digital mammography among women who participated in the Norwegian Breast Cancer Screening Program in 2002-08.

Four breast imaging specialists reviewed mammographic exams from interval and screen-detected cancers in two Norwegian counties, which included 49 interval and 86 screen-detected cancers on digital studies and 81 interval and 123 screen-detected film exams.

The percentage of missed interval cancers was 33 percent on digital and 30 percent on film, according to Hoff et al. The corresponding screen-detected miss rates were 20 percent on digital and 21 percent on film.

However, the researchers reported other differences. The average size of masses missed was significantly smaller on digital than on film for both interval and screen-detected cancers.

“There was a trend toward a lower percentage of masses with spiculated margins and a trend toward a higher percentage of masses with indistinct margins at digital than at film,” wrote Hoff and colleagues. The researchers noted the higher contrast resolution of digital makes it easier to distinguish a mass from surrounding glandular tissue. The higher contrast resolution of digital also improves the ability to perceive calcifications, which explains the higher percentage of malignancies with calcifications on digital than on film and lower percentage in prior mammograms of missed cancer.

In addition, there was a higher percentage of missed cancers with asymmetry at digital, which cannot be explained by the digital technique, according to the researchers. One possibility is that the use of postprocessing and large-screen monitors may have resulted in radiologists focusing on small details at the expense of overview. “To prevent pitfalls in digital reading, procedures should be implemented that emphasize the importance of viewing both standard and magnified views in a structured way,” wrote the researchers, who noted that computer-aided detection might assist in single-reader practices.

The researchers concluded by emphasizing the need for further studies exploring mammographic features of missed cancers in digital programs and underscoring the need for individual site reviews of interval and screen-detected cancers as part of ongoing quality assurance.