Should ultrasound be a routine part of cancer screening of women with dense breasts? An ongoing study being conducted by a New York City radiologist is adding statistical heft to the concept, indicating that ultrasound finds many nonpalpable occult lesions missed by mammography in women with dense tissue.
Ultrasound already plays a substantial role in breast imaging -- characterizing breast lesions, guiding biopsies, and monitoring therapy -- but has yet to be applied routinely in screening. One benefit of ultrasound is that its resolution isn't limited by dense tissue.
At the same time, it's well known that mammography has serious limitations in detecting cancers in women with dense breasts. Thus, adding ultrasound to mammography would seem to be obvious. However, one major impediment is cost: It would add additional expense to breast screening, which already suffers from low reimbursement rates.
At the American Institute of Ultrasound in Medicine conference in April, Dr. Thomas Kolb presented data on the subject from a study conducted over the past three and a half years at his private practice.
Kolb's initial work on the use of screening ultrasound for women with dense breasts was published in the April 1998 issue of Radiology; in his AIUM presentation, he presented data covering another 7,000 patients. He also presented new data comparing the sensitivity of ultrasound to mammography in women with dense breasts.
Kolb's goal was to see if ultrasound could visualize abnormalities not detected with mammography or physical exams. Over 42 months Kolb conducted consecutive screenings of 18,005 women. Of these, 6,242 women with dense breasts, normal mammograms, and normal physical exams received a screening ultrasound exam.
Others who had non-dense breast tissue and a normal mammogram did not receive an ultrasound exam. Those with either tissue type who also had a mammographic or palpable abnormality received ultrasound as part of the normal procedural work-up.
For the entire cohort of 18,005 women, 152 women were found to have 173 cancers, for a cancer prevalence rate of 8.4 per 1000 women.
Of the women with dense breasts and normal mammograms and physical exams, one-third had at least one mass, the majority of which were cysts. However, 330 women (5%) had solid masses and of those women 17 turned out to have 19 cancers. Therefore, screening ultrasound was able to detect three cancers per 1000 women. These cancers would have been missed by mammography and physical exams.
Further analysis of the data revealed the following:
- 13% of all cancers -- in women with both tissue types -- were detected only with screening ultrasound.
- 25% of the cancers (including ductal carcinoma in situ) in women with dense breasts were detected only with screening ultrasound.
- Excluding DCIS, 29% of all cancers in women with dense breasts were detected only with screening ultrasound.
- 37% of non-palpable cancers in women with dense breasts were detected only with screening ultrasound.
- If palpable masses and DCIS are excluded, 50% of all imaging-detected invasive cancers in women with dense breasts were detected only with screening ultrasound.
Sensitivity
Other new data Kolb presented concerned the sensitivity of mammography, which can be as high as 98% for breast tissue rated grade I on the American College of Radiology's density scale. However, Kolb found mammography's sensitivity dropped to 55% in women with the densest tissue, or grade IV. Conversely, ultrasound's sensitivity increases with breast tissue density.
In addition, mammography plus a physical examination still missed 30% of cancers in women with grade IV tissue, and 20% in all women with dense breasts. Mammography with screening ultrasound found 94% of all cancers in women with dense breasts.
"What can we conclude? In women with dense breasts, screening ultrasound can identify small, early-stage, otherwise occult cancers equal in size and stage to those detected mammographically," Kolb said. "If we can accept the associated cost and a false-positive rate of 5%, screening ultrasound should be an important adjunct to mammography in women with dense breasts."
Kolb referenced two recently published papers with similar results. One by Belgian researchers found breast screening with ultrasound alone found 12% of all cancers in all women, those with fatty and dense breast tissue. Meanwhile, an Austrian study of 6,113 women indicated that ultrasound screening found 23 cancers in 21 patients, for a detection rate of over 3 per 1000 screened, and a 37% increase in the number of nonpalpable breast cancers detected, in line with Kolb's numbers.
What about the cost of adding ultrasound exams to mammographic screening of women with dense breasts? For internal referrals, Kolb's facility charges $150 for a screening ultrasound, in addition to the cost of a mammogram. For patients just getting a screening ultrasound without a mammogram, Kolb charges $250.
Are the results worth the additional cost? Kolb declined to take a position, leaving this argument to healthcare economists. However, the efficacy of ultrasound in screening women with dense breasts is such that practitioners might want to reconsider use of physical exams, which produce poor results and lead to false positives, he said.
Over the long term, Kolb believes more studies are needed to determine ultrasound's role in breast screening.
"Screening ultrasound does not replace a mammogram," Kolb said. "It's applicable only for women with dense breasts, and at this point should only be performed by a physician, hopefully in the context of a study so that more data can be gathered."
By Brian Casey
AuntMinnie.com staff writer
May 2000
Related Reading
"Occult cancer in women with dense breasts: detection with screening US--diagnostic yield and tumor characteristics," Radiology 1998 Apr; 207(1):191-9
"Incidental findings on sonography of the breast: clinical significance and diagnostic workup," American Journal of Roentgenology, Vol. 173, 921-927."
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