Tomo boosts breast cancer detection, may cut false positives

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 - breast tomosynthesis
58-year-old woman with invasive ductal carcinoma (arrows) detected on screening mammography and digital breast tomosynthesis (DBT).
Source: American Journal of Roentgenology

Digital breast tomosynthesis coupled with 2D screening mammography improved the breast cancer detection rate compared with screening mammography only, according to a study published April 24 in The Lancet Oncology. However, the researchers preached caution and called for additional studies before applying the model in practice.

Given the documented shortcomings of conventional screening mammography, burgeoning potential of breast tomosynthesis as well as questions about selection bias in existing small studies of 3D mammography, trials of integrated 2D and 3D screening are needed.

Thus, Nehmat Houssami, MD, of Sydney Medical School in Australia, and colleagues devised Screening with Tomosynthesis OR Standard Mammography (STORM), a prospective comparative study that enrolled 7,292 asymptomatic women aged 48 years and older who attended population-based screening services in Italy from August 2011 to June 2011.

Women first underwent 2D screening mammography and then integrated 2D and 3D screening. Breast radiologists read the studies sequentially in the same day and recorded recall decisions independently for each exam.

Primary outcomes included the number of cancers detected, the number of cancers detected per 1,000 screens, the number and percentage of false-positive recalls and the incremental cancer detection rate provided by the integrated screening model. These were assessed by excision histology.

Houssami and colleagues also estimated the potential reduction in false-positive recalls if positive integrated 2D and 3D screening were used as a condition for recall.

A total of 59 breast cancers were detected in 57 women, with 39 detected at both 2D and 3D. An additional 20 cancers were detected with integrated 2D and 3D screening.

Integrated 2D and 3D mammography outperformed 2D alone, with the integrated protocol detecting 8.1 cancers per 1,000 screens versus 5.3 per 1,000 with the 2D approach.

Overall, 395 women had false-positive recalls at either 2D or 3D screening. False positives were higher with 2D mammography at 141 women versus 73 women with the combined approach. “Had a conditional recall rule [requiring positive 2D and 3D exams as a condition for recall] been applied we estimate that the false-positive rate would have been 3.5 percent and would have potentially prevented 68 of the 395 false positives,” wrote Houssami et al.

“We hope that our work might be the beginning of a new chapter for mammography screening: our findings should encourage new assessments of screening using 2D and 3D mammography and should factor several issues related to our study.”

Specifically, Houssami and colleagues focused on integrated screening; 3D screening without 2D might not produce the same results. Repeat screening with integrated exams was not assessed in the study and might yield a smaller effect on detection. And STORM did not address biological differences in cancers.

The integrated model requires a 2D and 3D acquisition that doubles the radiation dose, thus the model may not be justifiable unless it improves other outcomes in addition to detection, according to the researchers.

Houssami and colleagues issued a final caveat: “Our results do not warrant an immediate change to breast-screening practice, instead, they show the urgent need for randomized controlled trials of integrated 2D and 3D versus 2D mammography and for further translational research in breast tomosynthesis.”