JAMA: Screening US or MRI + mammo a boon for women at increased breast cancer risk
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Wendie A. Berg, MD, PhD, formerly of the American College of Radiology Imaging Network (ACRIN) in Philadelphia, and currently with the department of radiology at Magee-Womens Hospital, University of Pittsburgh School of Medicine, and colleagues conducted a study to determine the supplemental cancer detection yield of ultrasound and MRI in women at elevated risk for breast cancer.
The study included 2,809 women with increased cancer risk and dense breasts at 21 sites who consented to three annual independent screens with mammography and ultrasound in randomized order. Median age at enrollment was 55 years. Nearly 54 percent of women had a personal history of breast cancer. After three rounds of both screenings, 612 of 703 women who chose to undergo an MRI exam had complete data.
A total of 2,662 women underwent 7,473 mammogram and ultrasound screenings, 110 of whom had 111 breast cancer events. Fifty-three percent of cancers were detected by mammography, including 30 percent that were detected by mammography only; 29 percent by ultrasound only; and 8 percent by MRI only after both mammography and ultrasound screens failed to detect cancer. Ten percent of cancers were not detected by any imaging screen. A total of 16 out of the 612 women in the MRI substudy were diagnosed with breast cancer.
Among 4,814 incidence screens in the second and third years combined, 75 women were diagnosed with cancer. The researchers found that supplemental ultrasound increased cancer detection with each annual screen beyond that of mammography, adding detection of 5.3 cancers per 1,000 women in the first year; 3.7 women per 1,000 per year in each of the second and third years; and averaging 4.3 per 1,000 for each of the three rounds of annual screening.
Berg and colleagues acknowledged and addressed concerns about the harms of extra testing and biopsies for women who do not have cancer. “As has been observed with mammography and MRI, the risk of false positives decreased significantly with annual screening ultrasound in this study compared with the first screen.” But biopsy rates remained substantial for ultrasound-only findings, with 5 percent of women undergoing biopsy and only 7.4 percent of these women found to have cancer.
The addition of MRI screening further increased cancer detection, with a supplemental cancer detection yield of 14.7 per 1,000 women. However, “in a separate analysis of ACRIN 6666 participants, MRI was significantly less tolerable than mammography or ultrasound,” wrote Berg et al. Among ACRIN participants offered a screening MRI at no out-of-pocket cost, only 58 percent of women accepted.
The researchers cited high rates of induced testing, including biopsy, as a barrier; 7 percent of women in the study were biopsied based on MR findings.
Berg and colleagues identified other issues with MRI. That is, the clinically detected interval cancer rate is 8 percent in the main ACRIN 6666 protocol and all interval cancers remained node-negative at diagnosis.
“Despite its higher sensitivity, the addition of screening MRI rather than ultrasound to mammography in broader populations of women at intermediate risk with dense breasts may not be appropriate, particularly when the current high false-positive rates, cost and reduced tolerability of MRI are considered,” the authors wrote.
However, there are barriers to the adoption of screening ultrasound for women with dense breasts, according to Berg and colleagues. There is only one current procedural terminology code for breast ultrasound, and the Medicare reimbursement rate, approximately $90 for the global fee, does not cover the costs of physicians performing and interpreting screening ultrasound. In addition, there is a shortage of qualified breast ultrasound technologists.
Berg et al concluded by emphasizing that both supplemental screening methods were associated with increased cancer detection yield and an increase in false-positive results.