NEW YORKComputer-aided detection (CAD) of breast cancer
using digitized mammograms could have detected malignancies at least 1 year
earlier than film assessment by radiologists alone, according to findings from
the Elizabeth Wende Breast Clinic, Rochester, New York.
In a retrospective study, the investigators concluded that
"CAD has the potential to decrease the false-negative rate by more than
one-third," and in a prospective study they determined that if radiologists at
their clinic had acted on mammogram areas marked by CAD as suspicious, an
additional 16% of breast cancers would have been detected.
Stamatia V. Destounis, MD, a staff radiologist at the
Elizabeth Wende Breast Clinic and associate professor of radiology at the
University of Rochester, reported the results at a media briefing on advances
in breast cancer diagnosis and treatment, sponsored by the Radiological
Society of North America (RSNA) and held at Mount Sinai Hospital in New York
City. Both studies were recently published in the journal Radiology.
Dr. Destounis and her colleagues conducted a retrospective
study of 64,442 patients who had been screened for breast cancer at the
Elizabeth Wende Breast Clinic in the year 2000. Of 519 women with a breast
cancer diagnosed, 318 had had at least one prior mammogram 1 or more years
The investigators reviewed both prior and current films of
these 318 patients and identified 52 patients who had actionable
false-negative screenings that they believed were cancer.
The researchers used a commercially available CAD system to
assess whether the technique could enhance detection of breast cancer by
picking up cases that had been missed in prior film assessment by
CAD, which has been referred to as a second pair of eyes,
utilizes computer-learning software to highlight suspect areas on digitized
versions of mammography films, with distinct marks to indicate masses,
microcalcifications, and other areas for further investigation. The marks made
by CAD still must be interpreted by a radiologist.
Since 1995 at the Wende Clinic, all mammogram films have
been double-read independently by two radiologists, with the second
radiologist nonblinded to the diagnosis made by the first one. An internal
audit for 1996-2000 at the clinic revealed that double-reading alone had led
to a 9% increase in the number of detected breast cancers.
CAD Marked Missed Cancers
CAD marked 37 (71%) of the 52 cancers that had been missed
by double-reading at least 1 year earlier. Of these 52 cancers, CAD detected
cancer in 3 of 9 women who later returned to the clinic with breast cancer
symptoms (such as a lump, breast pain, or nipple discharge) and in 34 of 43
women who the investigators determined had received a false-negative
The investigators then assessed a variety of
patient-related and other factors to ascertain how those 52 cancers had been
missed. "We looked at the composition of the breast tissue, we looked at tumor
size, and we looked at lymph node metastasis," Dr. Destounis said. The
majority of false negatives, nearly 65%, were in dense breasts, with an
average tumor size of 8 mm on the earliest films vs 12 mm at final detection
CAD is not a perfect detector, she explained, in that only
34% (75 of 218) of marks actually turned out to indicate cancer: "For every
one mark that indicated cancer, there were two marks that were false
positive," she said. In its favor, however, CAD did correctly mark all three
of the patients who had lymph node metastases 1 year before these were
"We concluded that CAD had the potential to decrease the
false-negative rate" in the setting of a double-read of mammography films, Dr.
Destounis told ONI. With the 27 occult cancers included, conventional
assessment at the clinic yielded a 31% false-negative rate (98 of 318), yet
"if we had used CAD and actually been prompted by all the marks, it would have
reduced the false-negative rate to 19% [61 of 318]," she added.
Based on these retrospective findings, the investigators
initiated a prospective study to assess the positive predictive value of CAD
and the associated recall rate, by comparing breast screening outcomes as
performed by two radiologists vs one radiologist backed up by CAD.
The investigators enrolled 19,586 routine breast cancer
screening patients and analyzed them with CAD from November 2000 to July 2002.
In contrast to their standard mammogram-assessment procedure, the double-reads
for this study were double-blinded, so neither of a pair of radiologists
interpreting a film was aware of the other’s assessment. CAD was then applied
to film assessment by each reader. A total of 116 visible cancers were
Six More Cancers
"We found six more cancers by listening to the
computer-aided marks . . . which prompted us to work up an additional 7% of
cancers [with small-needle biopsy]," Dr. Destounis said. The mean size of the
cancers was 9.7 mm, all were invasive, and only 57% were minimal, meaning less
than 1 cm of invasion or any-size ductal carcinoma in situ.
"The conclusion we drew from this prospective trial is that
two doctors are still better than one doctor plus CAD, because two doctors
found 93% of the cancers and were prompted only 7% of the time; however, even
when we double-read, CAD did reduce our overall false-negative rate by 5%,"
she added. Two radiologists found 85 of 116 visible cancers, including
interval cancers (73%), and CAD marked 87 of 116 (75%).
Noting that radiologists do find many breast cancers with
high accuracy and reproducibility, she emphasized that film interpretation by
a radiologist supplemented with a second interpretation using CAD still
yielded "a 5% to 7% increase in the detection rate" achieved by
The problem, she said, is that radiologists don’t pay
enough attention to marks indicated by CAD. Although CAD marks potentially
malignant areas on a digitized film, radiologists "don’t always act on it. If
we had listened to CAD, we would have found another 16% of the cancers earlier
on. In order for us to get better, we have to find some way to have more
confidence in the computer and listen to the correct marks."
Dr. Destounis noted that CAD is becoming the standard of
breast cancer diagnosis in many hospitals, but she added that, while costs
will decrease over time, "CAD is an expensive up-front cost at $15 to $22 per
mammogram, the upkeep is expensive, and it does slow down the physician
because you have to decipher the marks and determine what’s important. CAD is
not meant to replace the doctor; it’s a tool to help us decide in threshold
cases whether to recall the patient or not."
Dr. Destounis said that she recommends CAD for all
mammograms. "There are multiple versions of CAD systems available, and, in
general, all are very good at finding the microcalcifications that indicate
early disease," she said. "And I think reimbursement is sufficient to cover
the extra cost associated with use of CAD."