Transitioning from analog mammography to full-field digital mammography (FFDM) is associated with a threefold increase in the detection of high-risk lesions. But it can also result in oversurveillance and overtreatment, according to a new study published in the November issue of the American Journal of Roentgenology.
Screening mammography has contributed to lower breast cancer mortality rates, as well as to the detection and characterization of precancerous lesions, wrote researchers from the University of Michigan. Before mammography screening programs were put into place, high-risk lesions such as atypical ductal hyperplasia or lobular neoplasia -- which can often manifest as calcifications -- were not as commonly diagnosed.
Dr. Colleen Neal from the University of Michigan.Digital mammography finds these lesions. But what should clinicians do once they're identified?
"If we're catching lesions earlier on the spectrum, we may be preventing malignancy, but the problem is, right now we don't have the means to determine which lesions could become invasive cancer," lead author Dr. Colleen Neal told AuntMinnie.com. "If we take all of these high-risk lesions to surgical biopsy and only 5% or 10% develop into cancer, are we overtreating?"
The University of Michigan transitioned from mainly using film-screen mammography in 2004 to using only digital mammography by 2010, and Neal and colleagues wanted to assess whether this transition was associated with increased detection of high-risk lesions.
For the study, the team included 142 cases of atypia or lobular neoplasia diagnosed in women with mammographic calcifications between January 2004 and August 2010. Neal and colleagues did not include lesions upgraded to cancer at excisional biopsy, those in women with ipsilateral cancer within two years of mammography, and any lesion that presented only as a mass (AJR, November 2013, Vol. 201:5, pp. 1148-1154).
Of the total cases:
- 82 (57.7%) were atypical ductal hyperplasia
- 17 (12%) were atypical lobular hyperplasia
- 25 (17.6%) were lobular carcinoma in situ (LCIS)
- 12 (8.5%) were atypia and LCIS
- 6 (4.2%) were other atypia
The group calculated the annual detection rate by dividing the number of high-risk lesions by mammography volume.
Digital mammography found almost twice as many high-risk lesions, Neal's team found. Of the 142 cases of atypia or lobular neoplasia, 52 (36.6%) were detected using film-screen mammography and 90 (63.4%) were detected using digital.
The detection rate was higher with digital mammography (1.24 per 1,000 exams) than film-screen (0.37 per 1,000 exams). The detection rate by year ranged between 0.21 and 0.64 per 1,000 mammographic studies for film-screen mammography and between 0.32 and 1.49 per 1,000 studies for digital.
"There was a big boost in high-risk lesions when we started taking off with digital," Neal said.
Digital mammography is steadily replacing film-screen, the team wrote: As of December 2012, 89% of mammography units in the U.S. were digital, compared with 8% in 2005, before publication of the Digital Mammographic Imaging Screening Trial (DMIST).
The transition to digital mammography has yielded positive effects, including identifying cancers in younger women with dense breast tissue. However, there may be disadvantages associated with digital mammography, including a higher screening recall rate and lower positive predictive value, according to the authors. And the diagnosis of high-risk lesions usually leads to a recommendation for surgical breast biopsy -- which is not without risk.
"Improved detection of high-risk lesions may allow enhanced screening, risk reduction treatment, and possibly breast cancer prevention," the team wrote. "[But] there are potential problems with increased diagnosis of high-risk lesions based primarily on the fact that progression of ductal carcinoma in situ and invasive cancer is not inevitable. The progression of high-risk breast lesions is unknown; many of these lesions may never manifest as clinically significant disease."
There's no going back to film-screen mammography now, so it's important for doctors to talk with their patients about the pros and cons of digital mammography, Neal said.
"We need to tell our patients that digital may find high-risk lesions, which then will put them on track for surgical biopsy -- which should not be undertaken lightly," she said. "Of course, I've never met a patient who, when I said to her, 'There's a chance that this lesion will never turn into a malignancy,' would be comfortable just leaving it alone."
