Mammography and Beyond Developing Technologies for the Early Detection of Breast Cancer (2001) / Chapter Skim
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1 Introduction
1 Introduction
Pages 15-54
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women, with more than 65,000 deaths annually (American Cancer Society, 2000; http: / /www3.cancer.org/ cancerinfo/~.
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. Currently, screening mammography is advocated in 22 countries.
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Screening for early cancer detection has been credited for part of the recent reduction in breast cancer mortality, which had been stagnant for 40 years (Blanks et al., 2000; Hakama et al., 1997; Mettlin, 1999; Peto et al., 2000) (Figure 1-2~.
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SOURCE: SEER Cancer Statistics Review, 1973-1996 (Ries et al., 1999~. Numbers are calculated using cancer incidence rates from the regions of the U.S.
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14~. The purpose of the study presented in this report was to review breast cancer detection technologies in development and to examine the many steps in medical technology development as they specifically apply to methods for the early detection of breast cancer.
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For instance, treatment outcome is often measured by using short-term surrogate end points that have previously been correlated with long-term outcome, but such surrogate end points generally do not exist for screening methods. There are many difficulties in accurately determining the real benefit of any cancer screening technology or program.
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Length bias reflects the fact that screening tests detect a disproportionate number of women with slowly progressing tumors. A cancer that takes several years to reach a palpable size will be detected as a smaller tumor by regular screening than one that grows to the same size in a much shorter time period.
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for breast cancer will be more likely to participate in screening trials and will be more compliant with the recommended guidelines for screening mammography. Since cancer screening may be more beneficial and cost-effective for high-risk populations than for the general popula
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BSE was first advocated in the 1940s and 1950s, before the advent of screening mammography. Breast surgeons saw many patients whose tumors were too large for surgical removal, and they believed that regular self-examination of the breasts would result in earlier detection when surgery was still an option.
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In Canada, a large randomized clinical trial has directly compared CBE alone with screening mammography plus CBE.5 The results showed no significant difference in breast cancer mortality rates between the two study arms at 7 and 13 years after the initiation of screening (Miller et al., 1993, 2000~6, although mammography identified smaller tumors than physical examination did. The study does not question the assertion that mammography lowers breast cancer mortality, but the results suggest that a very careful standardized physical examination (lasting an average of 10 minutes)
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There are now a variety of venues for mammography breast cancer screening, including doctors' offices, private radiology practices, hospital radiology departments, imaging centers, breast clinics, and mobile mammography vans. Because the effectiveness of screening mammography is dependent on the quality of the facilities and personnel, a federal law requires all mammography facilities to be certified by FDA.
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A diagnostic mammogram, which may include additional views or magnifications, is usually performed following a suspicious finding on a screening mammogram or when a woman has a new symptom such as a breast lump. To create a uniform system of assessing mammography results, the American College of Radiology developed the Breast Imaging Reporting and Data System (BIRADS)
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for pathological assessment of breast tissue (Fajardo and DeAngelis, 1997; Morrow, 1995; Scott and Morrow, 1999; Sneige, 1991~. A very thin needle and syringe can be used to remove either fluid from a cyst (standard FNA)
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The ABBI method uses a rotating circular knife and a thin wire heated with an electrical current to remove a large cylinder of tissue containing the abnormality. LIMITATIONS OF CURRENT TECHNOLOGIES Despite its demonstrated ability to detect breast cancer early and reduce disease-specific mortality rates to some degree, mammography has inherent limitations and risks like any cancer screening technology (including physical examination)
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Even when further evaluation rules out cancer, some women report impaired moods and daily functioning for up to 3 months after a suspicious finding on a mammogram (Lerman et al., 1991~. A study in Norway examined perceptions of quality of life 18 months following a false-positive mammogram.
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Lack of Data for Older Women The risk of breast cancer increases with age throughout a woman's lifetime, and the sensitivity and positive predictive value of screening mammography also improve as women age (Kerlikowske et al., 1993; Mushlin et al., 1998) (Table 1-4~.
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Results indicated an increased probability for detecting localized breast cancer in conjunction with a significantly reduced risk for detecting metastatic breast cancer among screened women (SmithBindman et al., 2000~. A case-control study from Holland found that regular screening mammography for women ages 65 to 75 was associated with a 55 percent reduction in mortality from breast cancer, although there was no reduction in breast cancer mortality associated with screening of women over age 75 (Van Dijck et al., 1996~.
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1.4b | | See fig. 1.4c Refer to surgeon , , , ACR Breast Imaging Reportir~g and ~ Datd System (BE 0 Assessment is incomplete; additional imaging needed.
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Statistical analysis of pooled data from seven randomized clinical trials indicated that screening mammography reduced breast cancer mortality by about 16 to 18 percent in women under age 50 (Berry, 1998; Kerlikowske 1997; National Institutes of Health, 1997~. However, the lag time between initiation of screening and clear demonstration of a reduced mortality was more than 10 years, whereas it was about 5 years for women over age 50.
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Radiation Sensitivity and Breast Cancer Screening Since mammography was first introduced, some concerns have been raised about the potential risks associated with repeated exposure of the breast to ionizing radiation (i.e., X rays)
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Of five studies conducted to date, only one reveals an increased risk for breast cancer in AT heterozygotes (Table 1-6~. In addition to these studies of early-onset or contralateral breast cancers occurring after radiation therapy, other study designs have thus far failed to reveal a significant role of AT heterozygosity as a risk factor for radiation-associated breast cancer.
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In contrast, between 1983 and 1992, DCIS constituted 12 to 18 percent of all newly diagnosed cases of breast cancer and may account for as much as 30 percent of breast cancer cases identified by screening mammography (Ernster et al., 1996~. Among women ages 40 to 49, as many as 40 percent of all cases of breast cancer detected by mammography are DCIS (Ernster and Barclay, 1997~.
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INTRODUCTION Lobules Lobules Normal duct Ductal carcinoma Invasive ducta in situ (DCIS) carcinoma Normal lobule Lobular carcinoma Invasive in situ (LCIS)
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. Increasing the ability to identify DCIS and LCIS raises important questions in regard to breast cancer screening.
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The fundamental support for these assumptions comes from the randomized clinical trials described earlier in this chapter, which showed that mammography screening of asymptomatic women results in early treatment of breast cancers that are detected and reduces disease-specific mortality by approximately 20 to 30 percent compared with that for women who have not been screened. Why is the decrease in mortality
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One might argue that improvements in imaging technologies might allow clinicians to increase the number of tumors detected at point B or even move detection to point C However, a second reason that reductions in breast cancer mortality rates due to screening mammography are limited might be embedded in the biology of the cancer itself.
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Nonetheless, recent randomized clinical trials have suggested that women with excised DCIS who do not receive further local (surgery, radiation) or systemic (hormonal)
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Screening mammo~ranhv 1 1 r- · ~ · 1 1 1 ~ 1 1 ~ ~ 1 · · ~ ~ 1 · ~ ~ has det~n~t~vely been shown to reduce, but not eliminate mortality from breast cancer when it is performed at regular intervals and followed by appropriate interventions. In randomized clinical trials, screening mammography reduced breast cancer mortality by about 25 to 30 percent among women ages 50 to 70 and by about 18 percent among women between the ages of 40 and 50.
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Mammograms are particularly difficult to interpret for women with dense breast tissue, who are at increased risk of breast cancer. The dense tissue interferes with the identification of abnormalities associated with tumors.
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It is also essential to understand what is being detected and how to appropriately intervene. Decisions about the use of new technologies should be firmly grounded in scientific evidence if investigators are to optimize the benefits and minimize the risks of early breast cancer detection.
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