Contribution of Clinical Breast Examination to Breast Screening Accuracy
Contribution of Clinical Breast Examination to Breast Screening Accuracy
Background There is controversy about whether adding clinical breast examination (CBE) to mammography improves the accuracy of breast screening. We compared the accuracy of screening among centers that offered CBE in addition to mammography with that among centers that offered only mammography.
Methods The cohort included 290 230 women aged 50–69 years who were screened at regional cancer centers or affiliated centers within the Ontario Breast Screening Program between January 1, 2002, and December 31, 2003, and were followed up for 12 months. The regional cancer centers offer screening mammography and CBE performed by a nurse. All affiliated centers provide mammography but not all provide CBE. Performance measures for 232 515 women who were screened by mammography and CBE at the nine regional cancer centers or 59 affiliated centers that provided CBE were compared with those for 57 715 women who were screened by mammography alone at 34 affiliated centers that did not provide CBE.
Results Sensitivity of referrals was higher for women who were screened at regional cancer centers or affiliated centers that offered CBE in addition to mammography than for women screened at affiliated centers that did not offer CBE (initial screen: 94.9% and 94.6%, respectively, vs 88.6%; subsequent screen: 94.9% and 91.7%, respectively, vs 85.3%). Mammography sensitivity was similar between centers that offered CBE and those that did not. However, women without cancer who were screened at regional cancer centers or affiliated centers that offered CBE had a higher false-positive rate than women screened at affiliated centers that offered only mammography (initial screen: 12.5% and 12.4%, respectively, vs 7.4%; subsequent screen: 6.3% and 8.3%, respectively, vs 5.4%).
Conclusions Women should be informed of the benefits and risks of having a CBE in addition to mammography for breast screening.
The Canadian Task Force on Preventive Health Care recommends that women aged 50–69 years undergo screening for breast cancer by mammography and clinical breast examination (CBE) every 1–2 years. Results of several randomized controlled trials have provided evidence that screening reduces the breast cancer mortality rate. Long-term follow-up of participants in these trials revealed a statistically significant reduction in mortality upon achieving 70% attendance among women in the target age group. Because most organized screening programs require a sufficient amount of time to reach a substantial proportion of the target population, initial evaluation of such programs includes evaluation of interim indicators of effectiveness, such as cancer detection rates and screening accuracy.
Measures of screening accuracy are particularly important interim indicators of the effectiveness of breast screening programs. Two such indicators, the cancer detection rate and screen sensitivity (which measures the proportion of women with cancer who had a positive screen), are used to determine whether screening is effective in detecting breast cancer in women. If the sensitivity is low, the test will miss many cancers, resulting in a high rate of false-negative results or interval cancers that contribute substantially to mortality in the screened population. Two other measures of screening accuracy, the referral rate and screen specificity, are related to the efficiency of the screening test and the need to perform as few procedures as possible on women who do not have cancer. If a screening modality produces a high proportion of false-positive results, then women may be inappropriately referred for further potentially invasive diagnostic tests. In addition, women who have a false-positive mammogram can experience anxiety, distress, and intrusive thoughts, which may persist for several months or years after the completion of assessment.
Although CBE can detect cancers that are missed by mammography, there is controversy on the value of adding CBE to mammography. A review of breast screening randomized clinical trials showed that mortality reduction in the four trials including CBE in addition to mammography was similar to those in trials including mammography only. A study of four Canadian provinces (including Ontario) that provide CBE found that CBE added to mammography had a small contribution to the early detection of breast cancer.
The accuracy of CBE can be affected by examiner experience and technique. A pooled analysis found that the accuracy of CBE varies according to factors related to the examiner, such as the duration of the examination, the examiner's experience, and the CBE technique used. The highest CBE sensitivity reported was achieved by the Canadian National Breast Screening Study-2, a randomized trial of women aged 50–59 years who were offered CBE alone or CBE and mammography, in which CBE was performed by specially trained health professionals who received a specific protocol for conducting breast examinations.
The Ontario Breast Screening Program (OBSP) is conducted under the auspices of Cancer Care Ontario and has operated since July 1, 1990, to deliver a population-based breast screening program. From 1990 to 1994, screening took place at nine regional cancer centers located across Ontario (including one in a mobile unit that targets communities in the northwestern region of the province). All nine regional cancer centers have dedicated breast screening centers that offer biennial screening consisting of two-view mammography and CBE performed by a nurse. Beginning in 1995, the OBSP began offering screening mammography and CBE at affiliated centers located within established mammography facilities in hospitals or independent health facilities. Centers that were affiliated with OBSP after April 1998 were encouraged but not required to offer CBE.
The OBSP provides a unique opportunity to evaluate the value of adding CBE to mammography alone for the detection of breast cancer. The purpose of this study was to compare the accuracy of referrals for further assessment made on the basis of CBE alone, mammography alone, and CBE and/or mammography among women who attended regional cancer centers or affiliated centers that provided mammography and CBE with the accuracy of referrals for further assessment among women who attended affiliated centers that offered mammography alone.
Abstract and Introduction
Abstract
Background There is controversy about whether adding clinical breast examination (CBE) to mammography improves the accuracy of breast screening. We compared the accuracy of screening among centers that offered CBE in addition to mammography with that among centers that offered only mammography.
Methods The cohort included 290 230 women aged 50–69 years who were screened at regional cancer centers or affiliated centers within the Ontario Breast Screening Program between January 1, 2002, and December 31, 2003, and were followed up for 12 months. The regional cancer centers offer screening mammography and CBE performed by a nurse. All affiliated centers provide mammography but not all provide CBE. Performance measures for 232 515 women who were screened by mammography and CBE at the nine regional cancer centers or 59 affiliated centers that provided CBE were compared with those for 57 715 women who were screened by mammography alone at 34 affiliated centers that did not provide CBE.
Results Sensitivity of referrals was higher for women who were screened at regional cancer centers or affiliated centers that offered CBE in addition to mammography than for women screened at affiliated centers that did not offer CBE (initial screen: 94.9% and 94.6%, respectively, vs 88.6%; subsequent screen: 94.9% and 91.7%, respectively, vs 85.3%). Mammography sensitivity was similar between centers that offered CBE and those that did not. However, women without cancer who were screened at regional cancer centers or affiliated centers that offered CBE had a higher false-positive rate than women screened at affiliated centers that offered only mammography (initial screen: 12.5% and 12.4%, respectively, vs 7.4%; subsequent screen: 6.3% and 8.3%, respectively, vs 5.4%).
Conclusions Women should be informed of the benefits and risks of having a CBE in addition to mammography for breast screening.
Introduction
The Canadian Task Force on Preventive Health Care recommends that women aged 50–69 years undergo screening for breast cancer by mammography and clinical breast examination (CBE) every 1–2 years. Results of several randomized controlled trials have provided evidence that screening reduces the breast cancer mortality rate. Long-term follow-up of participants in these trials revealed a statistically significant reduction in mortality upon achieving 70% attendance among women in the target age group. Because most organized screening programs require a sufficient amount of time to reach a substantial proportion of the target population, initial evaluation of such programs includes evaluation of interim indicators of effectiveness, such as cancer detection rates and screening accuracy.
Measures of screening accuracy are particularly important interim indicators of the effectiveness of breast screening programs. Two such indicators, the cancer detection rate and screen sensitivity (which measures the proportion of women with cancer who had a positive screen), are used to determine whether screening is effective in detecting breast cancer in women. If the sensitivity is low, the test will miss many cancers, resulting in a high rate of false-negative results or interval cancers that contribute substantially to mortality in the screened population. Two other measures of screening accuracy, the referral rate and screen specificity, are related to the efficiency of the screening test and the need to perform as few procedures as possible on women who do not have cancer. If a screening modality produces a high proportion of false-positive results, then women may be inappropriately referred for further potentially invasive diagnostic tests. In addition, women who have a false-positive mammogram can experience anxiety, distress, and intrusive thoughts, which may persist for several months or years after the completion of assessment.
Although CBE can detect cancers that are missed by mammography, there is controversy on the value of adding CBE to mammography. A review of breast screening randomized clinical trials showed that mortality reduction in the four trials including CBE in addition to mammography was similar to those in trials including mammography only. A study of four Canadian provinces (including Ontario) that provide CBE found that CBE added to mammography had a small contribution to the early detection of breast cancer.
The accuracy of CBE can be affected by examiner experience and technique. A pooled analysis found that the accuracy of CBE varies according to factors related to the examiner, such as the duration of the examination, the examiner's experience, and the CBE technique used. The highest CBE sensitivity reported was achieved by the Canadian National Breast Screening Study-2, a randomized trial of women aged 50–59 years who were offered CBE alone or CBE and mammography, in which CBE was performed by specially trained health professionals who received a specific protocol for conducting breast examinations.
The Ontario Breast Screening Program (OBSP) is conducted under the auspices of Cancer Care Ontario and has operated since July 1, 1990, to deliver a population-based breast screening program. From 1990 to 1994, screening took place at nine regional cancer centers located across Ontario (including one in a mobile unit that targets communities in the northwestern region of the province). All nine regional cancer centers have dedicated breast screening centers that offer biennial screening consisting of two-view mammography and CBE performed by a nurse. Beginning in 1995, the OBSP began offering screening mammography and CBE at affiliated centers located within established mammography facilities in hospitals or independent health facilities. Centers that were affiliated with OBSP after April 1998 were encouraged but not required to offer CBE.
The OBSP provides a unique opportunity to evaluate the value of adding CBE to mammography alone for the detection of breast cancer. The purpose of this study was to compare the accuracy of referrals for further assessment made on the basis of CBE alone, mammography alone, and CBE and/or mammography among women who attended regional cancer centers or affiliated centers that provided mammography and CBE with the accuracy of referrals for further assessment among women who attended affiliated centers that offered mammography alone.
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