Digital Mammography Trend Improves Cancer Detection Rates

A new study that set out to establish performance benchmarks for digital mammography screening suggests that the shift from film has improved cancer detection rates.

Researchers at the University of Vermont, Massachusetts General Hospital, and other institutions conducted a study to measure the performance of digital screening mammography, based on data collected from six Breast Cancer Surveillance Consortium (BCSC) registries that included 401,548 examinations of 265,360 women conducted between 2007 and 2013. Mammography indication and assessments by 418 radiologists in 92 radiology facilities were linked with cancer diagnoses from state cancer registries.

The researchers found that compared with the results from an earlier BCSC benchmarks publication, the cancer detection rate rose from 25.3 per 1,000 in 2005 to 34.7 per 1,000 in the new study. According to the researchers, the change may reflect improvements in mammography imaging technology, which permit the visualization of smaller lesions and greater detection of calcifications, resulting in increased cancer detection. But alongside the improved cancer detection rate, the abnormal interpretation rate rose from 8% in 2005 to 12.6%.

Another concerning trend was the drop in positive predictive value (PPV), from 31.5% in 2005 to 27.5% in the new study. The lower PPV results are a direct result of the abnormal interpretation rate increasing much more than the cancer detection rate, according to the researchers, suggesting that improvements in imaging may do more to permit the visualization of additional findings, but do not aid radiologists in discriminating between benign and malignant findings. The study was published on December 5, 2016, in Radiology.

“An increase in mammographic cancer detection does not necessarily have to come with a substantial rise in the abnormal interpretation rate. For instance, Europe has been able to achieve cancer detection rates similar to U.S. rates, with much lower abnormal interpretation rates,” said lead author Brian Sprague, PhD, of the UVM Cancer Center. “Increased utilization of double reading in Europe, where at least two radiologists interpret the same exam, may be a factor. In addition, variables like fear of litigation can affect abnormal interpretation rates.”

Digital mammography screening now includes digital breast tomosynthesis (DBT), which can increase breast cancer detection rates even further. DBT mammograms use low dose x-rays to create a three dimensional (3D) image of the breast, which can then be viewed in narrow slices, similar to CT scans. While in conventional 2D mammography overlapping tissues can mask suspicious areas, 3D images eliminate the overlap, making abnormalities easier to recognize. It is estimated that 3D DBT will replace conventional mammography within ten years.