We found that the screening CBE had very high specificity (>99%) among female health plan enrollees at average-risk of breast cancer. Although specificity of screening CBE was lower among women with increased breast cancer risk, it was still high (>97%) compared to clinical trials of breast cancer screening in which screening CBE specificity was approximately 94%. Diagnostic CBE was relatively nonspecific regardless of breast cancer risk.
Although screening CBE is recommended by some organizations and is commonly performed, few studies have reported screening CBE specificity in community practice. Specificity of screening CBE was 96.3% among women receiving screening CBE within a New England health plan that participated in our study.11
In contrast, higher specificities were observed among nurse examiners within a unique screening program within another participating plan12
and among screening CBEs performed by a single radiologist.8
In our study, screening CBE had similarly high specificity among a geographically diverse sample of women enrolled in 6 regional health plans who received CBE from diverse examiners.
Among a large sample of low-income women receiving examinations in the National Breast and Cervical Cancer Early Detection Program (NBCCEDP),7
the specificity of screening CBE was lower (96.2%) than among average-risk (99.1%) and increased-risk women (97.8%) in our study. Many women eligible to enroll in the NBCCEDP, however, may not have had recent previous examinations. Because of higher cancer prevalence among previously unscreened women, prevalence screens may have greater sensitivity but lower specificity than later rounds of screening. Thus, CBE performance among NBCCEDP enrollees may not generalize to populations receiving more regular breast cancer screening. In addition, data quality assessment of NBCCEDP claims may be limited. If a substantial fraction of enrollees with breast symptoms are misclassified as asymptomatic, estimates of screening CBE specificity based on NBCCEDP claims may be spuriously reduced.
The discrepancy in the specificity of screening CBE in the community and in clinical trials suggests that CBE conduct in actual practice may differ substantially from its conduct in experimental settings. The American Cancer Society recommends regular CBE screening based in part on clinical trial evidence that CBE can detect some cancers that are missed by mammography.20,21
In the trial achieving the highest CBE sensitivity (69%), trained examiners performed CBE in a systematic fashion with a usual duration of 5 to 10 minutes.22
The typical screening CBE in the community is probably less systematic and briefer,13
which may compromise sensitivity while boosting specificity. Indeed, the high specificity observed in our study is consistent with recent studies suggesting low sensitivity of screening CBE in community practice.7–10
Recent calls to standardize CBE conduct and reporting may be well-justified if screening CBE performance in community practice indeed falls short of performance in clinical trials.23
Specificity of screening CBE was significantly lower among women at increased risk for breast cancer. Patient history and perceived risk influence the interpretation of screening mammography.24
Clinical history may similarly lead clinicians to interpret subtle breast abnormalities more cautiously among women with risk factors for breast cancer. Clinicians might also conduct the examination more deliberately among these women, thereby increasing the likelihood of detection and subsequent evaluation of small breast lumps. Even so, the observed specificity of screening CBE among increased-risk women (97.1%) was still higher than among a general population within clinical trials of breast cancer screening (94%).6
Breast cancer is relatively common among women with certain breast symptoms,25
and cancer may be impossible to exclude based on physical examination alone. In this respect, the low specificity of diagnostic CBE may reflect good practice. Diagnostic CBE was significantly less specific among current estrogen users. This association could arise from estrogen effects on breast tissue or other characteristics of estrogen users that prompt further evaluation after diagnostic CBE.
The examinations in our study were performed from 1979 to 1992, and one might posit that current CBEs are of higher quality. However, we found no evidence of temporal trends in screening CBE performance and doubt that U.S. clinicians currently conduct the screening CBE differently. In addition, we studied a population of insured women aged 35–65 years with stable health plan enrollment, and our findings may not be generalizable to women outside this age range or who have different insurance statuses. Although our sample size is smaller than previous studies, precise estimates of screening CBE specificity do not require large samples because false-positive screens occur uncommonly. We found no significant association between menopausal status and specificity, yet breast density (which we could not measure directly) may affect CBE specificity independently from menopause.12
In addition, our study did not measure body mass index, which has been associated with lower sensitivity of screening CBE.9
Lastly, our study lacked detailed data on the reasons for diagnostic examination beyond the presence of symptoms or a previously positive test and included relatively few diagnostic examinations among average-risk women.
Our study has several important strengths, including a geographically diverse sample of women from 5 U.S. states who received CBE from a range of clinical examiners. In addition, careful ascertainment of examination purpose and breast cancer risk factors allowed us to estimate the specificity of both screening and diagnostic CBE and among both average- and increased-risk women. We studied a population receiving regular screening,11
rather than prevalence screening as in the NBCCEDP,7
which may provide more accurate estimates of CBE specificity among a general population of women receiving regular CBE screening.
Our study suggests that screening CBE in community practice has substantially higher specificity than in clinical trials of breast cancer screening. Diagnostic CBE, meanwhile, is relatively nonspecific. Our findings are consistent with other reports of high CBE specificity in unique settings8,12
and recent reports of low sensitivity in community practice.7–10
Discrepant performance of CBE in the community and clinical trials may reflect clinically important differences in examination conduct, duration, and interpretation among community clinicians compared to highly experienced examiners in experimental settings. While high specificity implies a lower risk of false-positive CBE, this benefit may come at the cost of lower sensitivity for breast cancer. Clinicians should try to perform CBE in a deliberate fashion like examiners in clinical trials, and women should be informed that a high-quality CBE may require minutes rather than seconds.