The Rational Clinical Examination
David L. Simel, Drummond Rennie
Breast Cancer
Mary B. Barton, Russell Harris, Suzanne W. Fletcher
Accuracy
Topics Discussed:
breast, breast cancer, criterion standard comparisons (diagnostic tests), palpation, physical breast examination, probability, sensitivity, specificity, women's health
Excerpt:
"To determine its accuracy as a screening test, CBE must be compared
with a criterion standard. Mammography cannot be that standard because
cancers that are missed by mammography can be found on CBE. Histology
alone also cannot be the standard because tissue will never be obtained
from all women whose abnormalities are detected by CBE. Even less
likely is the histologic examination of breasts that are normal
on examination to determine specificity. A compromise criterion
standard is to follow up all screened women for a defined period;
women diagnosed as having breast cancer must have histologic proof,
and all cases of breast cancer among women screened during the follow-up
period must be counted. This admittedly imperfect standard nevertheless
is so stringent that few studies of breast cancer screening22,25,32,33,67,68 meet
it.The sensitivity of the CBE is approximately 54%. The
specificity of the examination is about 94%.Clinical breast examination duration correlated significantly
with lump detection accuracy in experiments involving silicone breast
models. In 5 studies, mean examination duration was always longer
for examiners with higher sensitivity (Table 8-5).
The highest recorded sensitivity in human studies (69%)
was achieved in the NBSS, in which examiners took between 5 and
10 minutes to complete examination of both breasts.21On average, younger women have denser breasts that make lump
detection more difficult, whereas in older women, the breast becomes
more fatty, making lump detection easier.78 In
one referral population, examiners' sensitivity was 86% among
women aged 20 through 49 years and 96% among women aged
50 years and older.59 Silicone models simulating
postmenopausal breast tissue improved sensitivity over that in models
simulating premenopausal breast tissue (64% vs 51%).75 Two
large trials came to a different conclusion, albeit among women
in narrowly defined age ranges. The BCDDP found CBE sensitivity
of 53% among women between 40 and 49 years and 48% among
women between 50 and 59 years.22 The NBSS79 reported
higher CBE sensitivity in women aged 40 through 49 years (68%)
compared with those aged 50 through 59 years (63%), among
women receiving both mammography and CBE. Further study is needed
on this issue...."
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