NEW ORLEANSSteps can be taken to reduce the number of
false-positive results with screening mammography, W. Phil Evans, MD,
said at the American Society of Breast Disease annual meeting.
But false positives may not be such a catastrophe. Reducing the
false-positive rate should never overshadow the fundamental goal of
screening mammographythe early detection of clinically occult
breast cancer, said Dr. Evans, medical director, Susan G. Komen
Breast Center, Baylor University Medical Center, and clinical
associate professor of radiology, University of Texas Southwestern
Medical School, Dallas.
A study by Elmore et al (N Engl J Med 338:1089, 1998) called for new
methods to reduce the false-positive rate while maintaining
sensitivity. The study found that among 870 screened women, 24% had
at least one false-positive mammogram; 13%, at least one
false-positive clinical breast exam; and 32%, at least one
false-positive result for either test. Over 10 years, almost one
third of women screened for breast cancer will have a false-positive
False-positives add $33 to every $100 spent on screening. But
the bigger cost comes when cancer is not found, Dr. Evans said.
The average cost of treating early-stage breast cancer is about
$11,000 and for late-stage lesions, $140,000, with a reduction in
survival from 96% to 20%.
To reduce the number of false-positive mammograms leading to biopsy,
there must be a way to reduce the recall of patients in whom cancer
is not likely to be found, he said. To do so, one should obtain
previous mammograms for comparison, confidently and correctly
identify summation artifacts (tissue superimposed upon itself so it
incorrectly appears to be a mass), and learn to ignore subtle
mammographic findings of doubtful significance, Dr. Evans said.
One article reported 543 lesions of doubtful significance
from 5,514 mammograms, almost half of which were calcifications. The
lesions were evaluated about 30 months later, with the following
results: 74% did not change, 21% were less apparent or absent, 4%
were more apparent but not suspicious, and 1% (6 cases) were more
Of these 6 more suspiciouscases, 3 proved to be benign
without biopsy. Of the 3 that were biopsied, one was a low-grade DCIS
(Wolverton DE, Sickles EA: Am J Roentgenology 167:1041, 1996).
The conclusion was that it is almost impossible to
prospectively identify lesions that turn into cancer, Dr. Evans said.
To reduce the rate of requests for biopsies after full breast imaging
workup, Dr. Evans said that the radiologist must learn to confidently
and correctly identify those summation artifacts that require more
than standard screening views by properly tailoring the diagnostic
mammography. Doing spot compression views or changing the angle can
sometimes obviate the need for biopsy, he added.
Periodic mammographic surveillance can also be substituted for tissue
diagnosis for probably benign findings. Probably benign
describes lesions that have a 98% chance of being noncancerous.
Another method for reducing the false-positive rate is the use of
consensus double reading. Two radiologists independently interpret a
set of screening mammograms, then meet to discuss all abnormal
findings. They collectively discuss each case and reach a consensus
decision regarding which patients to recall for further evaluation.
Use of this method in one facility has resulted in 35% fewer and more
appropriate recalls, with a 50% increase in the number of cancers
detected at biopsy, Dr. Evans reported.
This technique does add to the cost of screening. It takes
about 4.5 additional hours of the radiologists time to
consensus double read 75 mammograms, adding about $500 a day, or
$100,000 annually, he said.
Systems for computer-aided detection, such as the ImageChecker System
(R2 Technology, Los Altos, California) may improve interpretation.
With this technology, computers digitize the mammogram, and a
computer algorithm searches for calcifications or crossing radiating
lines. Areas of concern are marked and reviewed by the radiologist.
A multicenter study has shown that computer-aided detection finds
many lesions overlooked by human interpretation, he said. There is no
increase in the overall recall rate but an increase in recalls of