Summary Dr. C.Bour, March 28, 2022
Tomosynthesis and annual screening: half of the women experience a false alarm
A study conducted by UC Davis Health* found that half of all women screened annually with tomosynthesis** experience at least one false-positive mammogram over a decade of screening.
Reminder: A false positive occurs when a mammogram is indicated as abnormal, but there is no cancer in the breast; this is after verification by other examinations (ultrasound, MRI, sometimes breast biopsy) and after a waiting period for the results between a few days and a few weeks.
Also, to be reminded, false positives in this screening are common. While approximately 12% of 2D screening mammograms are recalled for further investigation because of a false alarm, only 4.4% of these recalls, or 0.5% overall, result in a cancer diagnosis. Thus, women are most commonly alerted and recalled for nothing, resulting in significant moral harm.
* UC Davis Medical Center is part of a major academic health center located in Sacramento, California.
** Tomosynthesis (TDS): Tomosynthesis (or 3-D mammography) is an X-ray imaging technique that decreases the effect of breast tissue overlay by reconstructing a three-dimensional image of the breast from multiple low-dose X-rays acquired at different projection angles.
The objective of the study
This study aims to answer the following question: Is there a difference between screening with digital breast tomosynthesis (3D) vs. digital mammography (2D) in the probability of false-positive results after 10 years of screening?
This is a comparative effectiveness study of 903 495 individuals undergoing 2 969 055 screening examinations.
The study found that repeated breast cancer screening with 3D mammography only modestly decreased the risk of having a false-positive result compared with standard 2D digital mammography.
The 10-year cumulative probability of at least 1 false-positive result was 6.7% lower for tomosynthesis vs. digital mammography with annual screening and 2.4% lower for tomosynthesis vs. digital mammography with biennial screening.
Therefore, the risk of false positives is lower when screening is performed every two years instead of every year, but also in the case of non-dense breasts and for older women.
However, as can be seen, the difference is modest, and the reduction in false positives with 3D mammography is only 2.4% compared to standard mammography.
"Screening technology did not have a very large impact on reducing false positives," said Michael Bissell, an epidemiologist in the UC Davis Department of Public Health Sciences and co-leader of the study, on interview.
The first author notes, "We were surprised that the new 3D technology in breast cancer screening did not significantly reduce the risk of having a false-positive result after 10 years of screening; however, the risks of false-positive results are much lower with biennial screening compared with annual screening."
Contribution of this study
An earlier study was published in JAMA Oncol in 2018 and suggested that screening with the 3D technique was associated with better specificity (i.e., fewer false positives) and an increased proportion of breast cancers with a better prognosis (smaller and node-free) across all age and breast density groups. As the false positive rate was lowered, this resulted in a decrease in the number of repeat examinations.
We had analyzed this study here (only in French) and highlighted several limitations of this study, starting with the too-small size of the sample.
The over-detection problem remained unresolved since the claimed improvement in recalling rates was made at the cost of a significant over-diagnosis.
An article in the BMJ in July 2019 by Jeanne Lenzer, a science journalist, questioned the value of adding tomosynthesis to digital mammography, which she said was unproven. According to this author, the information given to women undergoing this technique, which is on the rise in the United States, is more of a marketing argument than neutral and scientific information.
3D technology has not been integrated into the French screening program due to the uncertainties highlighted by the French High Authority for Health.