Questions linger over clinical value of breast CAD

Computer-aided detection software may help radiologists spot more cancers, but CAD's clinical potential remains limited by its high false-positive rates.

Two studies presented at the ECR highlighted CAD's ability to boost single-reporting sensitivity and nearly match independent double-reading detection rates. Speakers failed to reach consensus, however, on the effect CAD's generally low specificity would have in clinical practice.

Researchers at Friedrich-Schiller University in Jena, Germany, used CAD in performing a retrospective analysis of 39 mammograms from patients whose breast cancer was initially overlooked. The software detected 22 of the 32 malignancies (68.9%), with a false-positive rate of 0.44 for masses and 0.31 for microcalcifications..

"Many issues are limiting the clinical use of breast CAD," said Dr. Ansgar Malich, a radiologist at Friedrich-Schiller University. "False-positive rates of CAD markers are still much too high, and there are questions whether this causes an increase in patients recalled for further examinations. However, in our own study, we did not see this result."

In another investigation, researchers at the Center for Studies into the Prevention of Cancer (CSPO) in Florence, Italy, tested early versions of competing commercial breast CAD systems against single- and double-read conventional mammography. Six radiologists reported 120 selected films (89 negatives, 31 interval cancers). Two weeks later, they assessed the same films with the help of CAD printouts from R2 and CADx software.

The results showed noticeable differences in the nature of the two software systems. The R2 software marked many more calcifications than the CADx system (218 versus 132), while the CADx printouts highlighted more masses than those from R2 (208 versus 105). Taken overall, however, both algorithms had similar sensitivity (70.9%) and a higher sensitivity than single reading without CAD (58.6%).

Both programs also flagged a large number of false alerts, translating to a small but significant increase in recall rate (from 18% to between 24% and 30%).

"The CAD companies should get together and pool their expertise to produce an algorithm that does well when detecting both microcalcifications and masses," said Dr. Stefano Ciatto, principal investigator at CSPO. "But we really need to look at the effect of using this software on recall. CAD will never be used alone, and radiologists should be able to filter out a lot of the false-positive noise."

The Florence study showed no significant difference in sensitivity between single reading with CAD and independent double reading of unmarked studies.

"Many retrospective studies show little difference in accuracy between CAD-assisted reading and double-reading," Ciatto said. "But like ours, these are retrospective studies on prepared film sets. What we need is prospective studies from a breast screening environment, though this would involve a lot of work to set up."