Three-dimensional mammography combined with conventional breast imaging can increase breast cancer detection by 27%.

The finding came from a team of experts at the University of Oslo in Norway and was published in the journal Radiology.

The researchers found that the detection rate for invasive and in situ cancers combined was 6.1 per 1,000 exams with traditional mammography, and with combined imaging, the rate was 8.0 per 1,000.

A 40% increase in invasive breast cancer detection was found when 3D mammography (tomosynthesis) was used in conjunction with traditional imaging, as well as a decrease of 15% in false-positives.

Per Skaane, MD, PhD, of the University of Oslo in Norway, and colleagues explained:

"The overall actual number of women recalled as a result of arbitration was larger for those initially assigned a positive score at mammography plus tomosynthesis. However, the concordant increase in the detection of 24 additional cancers resulted in a similar positive predictive value for the cases ultimately recalled for arbitration.

Because of the paired nature of the current study, these results could be biased against mammography plus tomosynthesis in that some of the dismissed cases initially referred on the basis of mammography alone might not have been dismissed if tomosynthesis had not been available at arbitration."

Mammography has been shown to decrease the number of deaths associated with breast cancer. In fact, one study demonstrated that mammography exams improve a breast cancer patient's chance of survival. However, it does have some shortcomings, for example, overlapping imaged tissue.

Therefore, many x-ray and non-x-ray imaging modalities have been examined supplements or substitutes for standard plain-film mammography.

Unconventional imaging methods that have been analyzed all have a common potential disadvantage - each is carried out as a separate method that needs technical and professional resources.

The scientists pointed out that the use of tomosynthesis has been limited by insufficiency of image reconstruction possible with 2D data sets.

With the emergence of a novel age of detectors, there is now a possibility to combine tomosynthesis into standard clinical practice.

Over 10 years ago, scientists showed how practical it was to use tomosynthesis in breast imaging, and recently, the FDA approved the first commercial system for clinical use.

Small retrospective reports that consisted of particular patient populations in experimental settings have been largely responsible for the clinical assessment of tomosynthesis.

In order to assess tomosynthesis in clinical practice, Skaane and team conducted a randomized clinical trial. The experts aimed to address 4 matters, including cancer detection rate with tomosynthesis, false-positive rate, the types of cancers detected by tomosynthesis, and positive predictive value for women recalled after arbitration of imaging results.

The team examined a subgroup of Norwegian females who signed up to participate in an ongoing program for breast cancer screening. A total of 12,631 subjects were screened using both tomosynthesis and 2D mammography.

Screening involved viewing each breast twice by tomosynthesis and digital mammography, adding approximately 10 seconds to image acquisition for each view.

The radiation dose doubled with combined imaging, as opposed to mammography by itself. However, it still was under safety limits.

Four radiologists used their expertise to individually analyze each image. A positive score was considered ≥2, and all of the scores were reviewed to reach an agreement.

A total of 12,621 subjects were included in the final results. 77 cancers were detected by using mammography, but the detections rose to 101 with mammography combined with tomosynthesis (a 31% increase).

A ratio of 1.27 resulted from a modification for reader-specific performance levels for combined imaging vs. mammography by itself.

The rate of false-positives with mammography was 6.1 per 1,000 screenings, and with combined imaging, the rate was 53.1 per 1,000 - a 13% decrease in false-positives (which rose to 15% after adjustment).

The researchers found that mammography plus tomosynthesis detected 81 invasive cancers compared to 56 with mammography by itself (a 40% improvement). The detection of higher-grade cancers also improved with the use of tomosynthesis by 26%.

After adjudication 265 women were recalled, of whom 77 had cancer, and 351 with combined imaging, of whom 100 had cancer - i.e. the positive predictive values were 29.1% and 18.5% respectively.

The researchers concluded:

"These results suggest that, despite the fact that the number of cases assigned a positive score before arbitration and recalled after arbitration was greater with mammography plus tomosynthesis, there was no substantial decrease in the positive predictive value in these patients."

Written by Sarah Glynn