Digital mammography fails to improve detection of deadly breast cancers
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Twenty years ago, digital mammography seemed poised to take its place at the forefront of breast cancer imaging.
Studies indicated the screening technology, approved by the FDA in 2000, had the potential to reduce callbacks for positive findings, and many speculated that it would detect more disease and lead to fewer interval cancer diagnoses than film mammography.
However, according to study results published in JNCI: Journal of the National Cancer Institute, the small increase in cancer detection conferred by digital mammography did not equate to a decrease in the rate of interval cancers, or those diagnosed between screenings.
“Interval cancers are representative of cancers that are fast-progressing and have become clinically detectable,” study author Rachel Farber, MPH, of the faculty of medicine and health in the School of Public Health at University of Sydney in Australia, said in an interview with Healio. “If the increase in detection rate has increased the clinical utility of screening, then we would hope to see a subsequent decrease in the interval cancer rate. This would suggest that some of the additional screen-detected cancers were clinically important and otherwise would have rapidly progressed if left undetected.”
Evaluating the impact
In the systematic review and meta-analysis, Farber and colleagues reviewed seven databases for published studies that evaluated film vs. digital mammography among the same population of asymptomatic women. They assessed detection, recall and interval cancer rates to determine whether the newer technology yielded improved health outcomes.
They identified 24 studies with 16,583,743 screening examinations (film, n = 10,968,843; digital, n = 5,614,900), seven of which measured interval cancers.
Results showed a cancer detection rate increase of 0.51 (95% CI, 0.19-0.83) per 1,000 screens and a recall rate increase of 6.95 (95% CI, 3.47-10.42) per 1,000 screens with digital vs. film mammography. Researchers observed a greater relative increase in the detection rate for ductal carcinoma in situ (25.2%; 95% CI, 17.4-33.5) than for invasive cancers (4%; 95% CI, 3-13).
Among the studies that reported interval cancers, researchers observed no change in the interval cancer rate per 1,000 screens following the switch to digital mammography (0.02; 95% CI, 0.06 to 0.03).
“There’s a default we always have that new must be better,” Otis W. Brawley, MD, MACP, Bloomberg Distinguished Professor at Johns Hopkins School of Medicine, a HemOnc Today Editorial Board Member and co-author of a related editorial, said in an interview with Healio. “In this instance, new is better at finding lesions, but some of those lesions are not the ones that kill. The big issue is that we in America have had tremendous difficulty with the concept that there is something that occurs in people’s breasts, prostates and lungs which, when biopsied, looks like cancer, but in that individual, is not destined to grow, spread and kill. That’s what we call overdiagnosis.”
Farber said a radiologist learning curve has been suggested as a potential explanation for the increased recalls with digital mammography. She added that in the Netherlands, recall rates increased but stabilized as radiologists became more familiar with the digital technology.
“Under this notion, some of the other included studies excluded the first screening round or results from the first 6 months after the changeover,” Farber told Healio. “However, these exclusions from recall data negate the fact that real women were recalled during that time. Further, [although] recall rates may stabilize in some instances, in many cases they may not have had a chance to reach a steady state before a new technology is introduced. A new technology’s effect on recalls, even temporarily, needs to be considered when weighing the benefits and harms.”
Looking beyond imaging
Farber emphasized that the study was not intended to make a case against digital mammography, which has clear benefits.
“Digital mammography takes an electronic image of the breast and allows images to be stored and transmitted electronically. This provides significant technical and practical advantages over film in the provision of population screening programs and allows for potentially decreased time between screening and results,” Farber told Healio. “No one is suggesting that mammography return to film, but rather use this example to emphasize the importance of carefully considering benefits and harms before adopting a new technology.”
Brawley said it may be possible to refine digital mammography technology so that it can better detect invasive cancers, but he added that other approaches to detection should be investigated.
“Maybe they can tweak digital mammography and make it such that it is finding more disease that needs to be cured,” Brawley told Healio. “Maybe we have gone as far as we can go with imaging, and we need to look at some other types of screening. There’s some very interesting work now having to do with circulating DNA. Maybe we need to go beyond imaging.”
Farber said one technology being explored for worldwide use in population screening is tomosynthesis, or 3D mammography. The ongoing, NIH-sponsored TMIST trial is comparing tomosynthesis with conventional 2D mammography for breast cancer screening.
“The existing evidence indicates that tomosynthesis improves initial screen detection measures such as cancer detection and/or recall rates,” Farber said. “However, new research in tomosynthesis screening should focus on evaluating both the short-term and the intermediate- to long-term outcomes, including effect on interval cancer rates.”
Brawley said he believes the first step in rectifying digital mammography overdiagnosis is to recognize that newer technology is not necessarily superior.
“The first thing we have to do is realize that we may have pushed imaging to its limits,” he said. “The second thing we need to do is stop overpromising the value of digital mammography right now.”
Reference
For more information:
Otis Brawley, MD, MACP, can be reached at Johns Hopkins University, 1550 Orleans St., CRB 1M-14, Baltimore, MD 21287; email: otis.brawley@jhu.edu.
Rachel Farber, MPH, can be reached at Camperdown NSW 2006, Australia; email: rachel.farber@sydney.edu.au.
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