Breast Cancer: Strategies for the 1990s 1

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Mammography and Breast Cancer Screening Lawrence W. Bassett, MD, * Viken Manjikian III, MD, t and Richard H. Gold, MD:j:

Breast cancer continues to be the most common cancer in American women, and its incidence is increasing. In the United States in 1990, an estimated 150,000 new cases will occur, and 44,000 women will die of the disease. 98 The greatest risk is for women over the age of 40 years, and the incidence increases progressively until the age of 70. Although some women are known to be at higher risk (see article by Lynch and associates), 75 per cent of women who develop breast cancer have no known risk factors other than increasing age. 87 The best hope for improving survival is early detection, and the most successful method of breast cancer screening for both earlier detection and decreased mortality rate is mammography. 4, 70, 106, 107 It is estimated that, on the average, a mammogram detects a breast cancer 2 years before it is palpable.

EVOLUTION OF MAMMOGRAPHY

In 1913, Albert Salomon, a German surgeon, reported his experience with radiographs of a large number of excised breasts. 86 He was able to distinguish some infiltrating from noninfiltrating carcinomas and to recognize some nonpalpable breast cancers. Stafford Warren, a radiologist at the University of Rochester, pioneered clinical mammography in the 1930s.u4 However, mammography was never widely used because of technical difficulties. In the 1950s, Raul Leborgne in Uruguay revitalized interest in mammography when he reported the radiographic appearance of carcinoma microcalcifications and performed histopathologic correlations. 65 Further *Professor of Radiological Sciences, UCLA School of Medicine, and Director, Iris Cantor Center for Breast Imaging, UCLA Medical Center, Los Angeles, California tDepartment of Radiological Sciences, UCLA School of Medicine, Los Angeles, California tProfessor of Radiological Sciences, UCLA School of Medicine, Los Angeles, California

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work was done in the 1950s by Jacob Gershon-Cohen in Philadelphia, who identified many features of benign and malignant lesions. 43. 44 In 1960, Robert Egan in Houston introduced a reproducible method of obtaining diagnostic x-ray examinations of the breast using a highmilliamperage, low-kilovoltage technique and industrial film. 29 In the mid1960s, the first x-ray unit designed for mammography was introduced by Gros in Strasbourg, France. 50 This dedicated mammography unit used a molybdenum anode for better soft-tissue imaging and a breast compression device to eliminate motion and improve image quality. Another important advance came in 1972 with the introduction of film-screen mammography, which permitted rapid automatic processing, shorter exposures, and sharper images. us Having its origin in experimental studies undertaken as far back as 1952,83 xeromammography became commercially available in 1972 largely because of the work of John Wolfe. Xeromammography improved image quality by enhancing the edges of high-density structures, particularly spiculations and calcifications. 48 Early mammograms resulted in a radiation dose of approximately 1 to 4 rads. Today, a two-view film-screen examination leads to an average glandular dose of 0.04 to 0.08 rads, whereas xeromammography (negative mode) results in 0.3 to 0.5 rads. 71 Clinical investigations have revealed no significant difference in the diagnostic accuracy of film-screen and xeromammography.80. 99 Magnification techniques improve the quality of both xeroradiographic and screen-film recording systems. 90 Limited by its higher radiation doses, the role of magnification mammography is to supplement conventional studies that show equivocal findings. A 1986 survey conducted by the American College of Radiology indicated that the majority of radiologists were using film-screen mammography.13 In this survey of 319 radiologists, 54 per cent were using filmscreen mammography, 30 per cent were using xeromammography, 16 per cent were using both, and only 0.3 per cent were still using direct (non screen) film mammography. Seventy-two per cent of the radiologists had changed their method during the preceding 10 years: more than 50 per cent had changed from xeromammography to film-screen mammography, and another 23 per cent had switched from nonscreen to film-screen mammography. As a result of declining sales, the Xerox Company, in February 1989, announced that it would discontinue the production of xeromammography equipment.

PERFORMING THE EXAMINATION The breast can be imaged in various directions. Film-screen mammography has three primary views: oblique, lateral, and craniocaudal. 47 Recent reports have identified the oblique projection as the most effective of these. 3. 6. 67 Its superiority is attributable to the fact that it is the view that most thoroughly depicts the deeper structures of the upper outer quadrant and axillary tail. 6 The oblique view is obtained by directing the x-ray beam perpendicular to the pectoral muscle in a superomedial to inferolateral

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direction (Figs. 1 and 2). A true lateral view can be obtained with the xray beam directed from medial to lateral or lateral to medial, and it is used in conjunction with the craniocaudal view to determine the exact location of a breast lesion. In the craniocaudal view, the beam is directed 90 degrees from the lateral. A chest wall view, which includes juxtamammary structures, is often used for xeromammographyID (Fig. 3). In the past, some investigators have suggested a single-view screening examination to reduce radiation exposure, cost, and examination time. 19. 68 However, others have found the rate of cancer detection is too low with single-view examinations, with as many as 11 per cent of lesions being missed. 3, 77 A significant limitation of single-view screening is that a cancer is frequently obscured by overlying parenchymal tissue in one projection, yet visible in another. Because greater numbers of patients need to be called back for additional views, single-view screening may actually be less cost effective than two-view examinations. 9, 96 In fact, a second view does not significantly increase the risk, cost, or time of screening,96 and it enhances diagnostic ability. In one study, oblique, lateral, and craniocaudal views were obtained on 9662 patients. 12 Of 172 cancers found, 125 were seen on all three views, 11 only on the oblique view, 4 only on the lateral view, and 3 only on the craniocaudal view. Ten were not depicted on any view. Cancers were missed in individual radiographs because they were masked by overlying dense parenchyma or because the image did not include the abnormal area. Two-view oblique-craniocaudal mammograms showed 158 of the 172 cancers, whereas lateral-craniocaudal combinations showed 151. Special views, such as exaggerated inner or outer craniocaudal views, and spot compression films, restricted to a specific area of interest, are used to define a lesion better or to verify its presence. 46 Adequate breast compression is essential for high-quality mammo-

Figure 1. Mediolateral oblique view for mammography. The filmscreen combination is placed under the breast parallel to the plane of the pectoral muscle, and compression is applied parallel to the muscle.

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Figure 2. Right and left mediolateral oblique views. A, In a 40-year-old woman, the breasts contain mixture of dense parenchymal tissue and radiolucent fat. The image includes the pectoral muscle (arrow), ensuring that as much of the breast as possible is shown. B, In a 65-year-old woman, the breast is composed almost completely of radiolucent fat, allowing for the greatest possible accuracy.

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Figure 3. Xeromammogram; chest wall view.

grams. 47, 71 Compression holds the breast motionless, separates tissues to disclose small lesions, improves image quality by decreasing scattered radiation, and reduces the radiation dose by decreasing breast thickness. THE NORMAL BREAST

The breasts of younger women are usually radiopaque because they are composed primarily of dense fibroglandular tissue (Fig. 2A). When severe, this radiopacity significantly limits the accuracy of the mammographic examination. 33 With increasing age and after childbearing, the dense glandular tissue is replaced by radiolucent fat, allowing abnormalities to be detected more readily (Fig. 2B). The breast tissue should be relatively symmetrical bilaterally. Surgery, fibrocystic changes, and a desmoplastic response to carcinoma can create asymmetry. Thus, mammograms should be viewed such tllat the right and left breasts can be compared easily (Fig. 2). QUALITY ASSURANCE

A 1986 survey of 319 mammography facilities conducted nationwide indicated regular monitoring of mammography dosage by only 71 per cent. 13 A 1988 inspection of 96 mammography units in 80 facilities in Michigan by

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the Michigan Department of Public Health revealed additional problems. 97 Of the 96 units, 34 did not detect the appropriate number and size of lesions in a breast phantom, 8 exceeded acceptable radiation exposures, and 36 had other deficiencies. Concerns of radiologists, local and national medical organizations, and the public have led the American College of Radiology (ACR) to develop a voluntary mammography accreditation program. This program offers radiologists the opportunity for peer review and evaluation of equipment, staff qualifications, image quality, and radiation dosage. To receive accreditation, each facility must be under the direction of a Board-certified radiologist, and the radiologic technologists must either be certified by the American Registry of Radiologic Technology or have an equivalent state license. Mammograms should be performed only with dedicated equipment, or, for xeromammography, with general purpose equipment that has been adequately modified. The x-ray facilities must purchase a breast phantom for use in the accreditation process and ongoing quality-control procedures. Radiographs of the phantom and thermoluminescent dosimetry chips and mammograms of two patients are evaluated by a review panel of experts. Certification by the ACR Mammography Accreditation Program may become the standard by which mammography facilities will be deemed acceptable by referring physicians, consumers, and local and national organizations. By July 1989, more than 1100 of the approximately 8000 mammography facilities nationwide had applied for Mammography Accreditation, and more than 500 had been accredited. Many states have their own certification programs for mammography equipment and image quality, coordinated by their own regulatory boards for radiologic health. Additional quality assurance programs may be under the jurisdiction of county and city services. FEATURES OF MALIGNANT AND BENIGN LESIONS The mammographic features of malignancy can be divided into primary, secondary, and indirect signs. The primary signs include a mass of relatively high radiographic density, microcalcifications, or both. Secondary signs, such as skin thickening and retraction, are usually obvious clinically and will not be discussed here. Subtle indirect signs that may be the only evidence of a nonpalpable cancer include architectural distortion and the appearance of a neodensity. Malignant Masses An irregular or spiculated margin is the most important mammographic feature indicating that a breast mass is malignant (Fig. 4). The more highly infiltrative the lesion, the more spiculated the margin will appear in the mammogram. 45, 105 Malignant Calcifications Malignant calcifications may occur with or without a mass. 30, 40, 66. 101 The microcalcifications are typically numerous and clustered, of various

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Figure 4. Close-up of mammogram shows typical features of malignancy in infiltrating ductal carcinoma with calcifications. The tumor mass (asterisk) is dense and is associated with numerous clustered calcifications (arrows), both within and separate from mass, which differ in size and shape and form casts of the ducts.

sizes and shapes, and may have a branching configuration (Fig. 4). The greater the number of calcifications in a cluster, the greater the likelihood of malignancy. 79 A cluster can be defined as three or more calcifications in an area 0.5 cm2 • Indirect Signs of Malignancy As many as 20 per cent of nonpalpable breast cancers may be identified on mammograms by subtle indirect signs. 73, 92 These include architectural distortion (Fig. 5A), parenchymal asymmetry (Fig. 5B), a unilateral focus of one or more prominent ducts, and a developing neodensity (Fig. 6).73, 92 To recognize these signs, it often is necessary to have previous mammograms for comparison. Unnecessary biopsies can often be avoided when the findings are unchanged from earlier examinations. Therefore, mammograms should be retained as long as possible. Benign Masses In contrast to the infiltrative margins of most carcinomas, the majority of benign masses, such as cysts, intramammary lymph nodes, and fibroadenomas, have sharply circumscribed margins (Fig. 7). Benign Calcifications Benign calcifications are more often evenly scattered than clustered. Benign secretions within the ducts manifest calcifications that are thick and linear or ring like (Fig. 8). Calcifications of fibroadenomas are usually coarse (Fig. 7). Post-traumatic fat necrosis may result in calcification in the wall of a radiolucent cyst (Fig. 9).

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Figure 5. Indirect signs of malignancy. A, Architectural distortion. A subtle area of spiculation (arrow) without an obvious mass is present in the upper hemisphere of the breast. At biopsy, this proved to be a small ductal carcinoma with a marked desmoplastic reaction. B, Asymmetric density. In a 34-year-old woman, an asymmetric region of parenchymal distortion and increased density (arrow) is present in the left breast. Biopsy revealed a small focus of noninvasive ductal carcinoma. Increased density in the mammogram was secondary to desmoplastic and inflammatory responses to tumor.

Pitfalls in Mammographic Interpretation Although masses with spiculated or ill-defined margins are usually malignant, a similar appearance may be seen in association with benign radial scars, sclerosing adenosis, post-traumatic fat necrosis, or surgical scars (Fig. 9). Less infiltrating cancers may have only slightly irregular or even well-circumscribed margins. Occasionally, a carcinoma is so well circumscribed that it resembles a benign lesion. Papillary, medullary (Fig. 10), and colloid (mucinous) carcinomas are particularly likely to be well circumscribed. 8 The calcifications of fibrocystic changes often mimic those of malignancy, leading to unavoidable false-positive mammograms. Calcific-like

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Figure 6. Developing neodensity. A, Screening mammogram in 1982 is normal. B, Screening mammogram 1 year later shows poorly defined neodensity (arrow). Biopsy revealed infiltrating ductal carcinoma.

deposits in the skin secondary to tattoos, deodorants, ointments, or sebaceous gland secretions can also be mistaken for malignancy. Therefore, clustered microcalcifications are a sensitive but not a specific sign of malignancy.

POSTOPERATIVE AND POSTRADIOTHERAPY CHANGES IN THE BREAST Postoperative or postradiotherapy changes include skin thickening or retraction, architectural distortion, asymmetry, calcification, and fat necrosis (see Fig. 9).18. 20. 82. 103 Some of these postoperative abnormalities may be mistaken for carcinomas. 93 Therefore, for comparison purposes, it is helpful to perform a baseline postoperative or preradiotherapy mammogram and regular mammographic follow-up at intervals of 6 months to 1 year.

PREBIOPSY NEEDLE LOCALIZATION Mammographically guided needle localization is indicated for biopsy of any suspect lesion seen in mammograms but not identified on clinical

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Figure 9. Fat necrosis after lumpectomy and radiotherapy. A, Twelve months after surgery. The skin is thickened and retracted (arrow). There is a ring-like cyst (arrowheacf), which is filled with radiolucent fat and microcalcifications. On the boundary of the cyst, there is a spiculated parenchymal scar (asterisk). Below are typical coarse calcifications in the wall of another lipid-filled cyst (broad arrow). B, Follow-up 1 year later. Microcalcifications (arrow) are now coarse and typically benign. The parenchymal scar has not changed.

adversely affected when a biopsy is delayed because of a negative mammogram. 21,31,35,117 In one study, 36 women with breast masses and negative mammograms had eventual biopsy-proved malignancy.72 Of the 17 who had biopsies performed within 2 months of their negative mammograms, 3 had

Figure 10, Well-circumscribed carcinoma mimicking a benign mass. A lobulated, well-defined mass is seen in the breast of 60-year-old woman. Biopsy revealed medullary carcinoma.

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Figure 11. Perforated compression plate is used to direct needle aspiration cytology or placement of localization hookwire for biopsy of non palpable lesions.

extension to the axillary nodes, whereas of the 19 who had biopsies delayed from 3 to 24 months (mean 12 months), 11 had axillary node involvement. Thus, mammography should not be considered a substitute for biopsy in the presence of suspect clinical findings. Dense parenchymal tissue is the principal cause of false-negative mammograms. 59 Other sources of error include mistaking a well-circumscribed carcinoma for a benign mass; mistaking malignant calcifications for benign ones because they do not show the rod, curvilinear, or branching shapes that are characteristic of malignancy; and not recognizing the indirect signs of malignancy.92 Another source of false-negative results is faulty radiographic technique. 73

MAMMOGRAPHY FOR BREAST CANCER SCREENING The first randomized controlled study of screening mammography was undertaken by the Health Insurance Plan (HIP) of Greater New York from 1963 through 1967. 89 Women were offered annual screening by physical examination and mammography for four successive years. Mter 7 years, there was a 30 per cent reduction in the breast cancer mortality rate in the women offered screening compared with those in the control group. After 18 years, the mortality rate was still reduced by 25 per cent. If mammography had been omitted from the annual screening, the benefit would have fallen by one third. 88 , The Breast Cancer Detection Demonstration Project (BCDDP), sponsored by the American Cancer Society and the National Cancer Institute, enrolled 280,000 women. From 1973 through 1978, five consecutive annual

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Figure 12. Hookwire localization of nonpalpable mass and calcifications. A, Craniocaudal mammogram performed with perforated compression plate. Needle will be placed through the hole most directly over the lesion (arrow). B, Lateral mammogram confirms placement of the needle close to the lesion. J-Shaped hook anchors the needle in place. C, Specimen radiograph verifies that suspect mass and calcifications have been excised.

screenings were conducted using physical examination and mammography. As this was a demonstration project and not a population-based randomized control study, definitive conclusions about the value of screening cannot be derived from the data. Howeve r, the results do reflect the striking improvements in mammography that had taken place since the New York study: Mammography detected 91 per cent of all the cancers found by screening. 4 Forty-two per cent of the lesions were detected only with mammography, compared with 33 per cent in the earlier study. Nine per cent were

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Figure 13. Multicentric carcinoma. Close-up of mammogram of palpable carcinoma (arrow), which is dense and has an irregular margin. Nonpalpable calcifications (arrowheacl) represented a second focus of carcinoma.

detected only by physical examination, compared with 44 per cent in the earlier study. One third of the cancers were noninfiltrating or infiltrating but less than 1 em in size, and most of these were detected only by mammography. In contrast, none of the cancers detected by screening in the New York study was less than 1 em in size. Less than 20 per cent of all the cancers detected in the Demonstration Project had spread to the axillary lymph nodes; the incidence of nodal involvement was only half that of other newly diagnosed breast cancers in the general population. Several European studies have confirmed the value of mammographic screening. The first was a Dutch case-control study in which all women over 35 in Nijmegen were invited to participate in single-view mammography every 2 years. 113 From 1975 through 1982, the mortality rate from breast cancer was reduced by 52 per cent. A second Dutch case-control study, at Utrecht, involved women ages 50 to 64 who were screened initially and then at 12, 18, and 24 months.24 In this study, the mortality rate was decreased by 70 per cent. A population-based randomized control study in Sweden began in 1977 with single-view screening at 24- to 33month intervals. 106, 107 After 7 years, there was a 31 per cent decrease in

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the mortality rate in the screened group, and there were 25 per cent fewer stage II and greater cancers in the women who were screened.

INDICATIONS FOR MAMMOGRAPHY AND GUIDELINES FOR SCREENING Mammography is indicated whenever there are suspect clinical findings and prior to any breast biopsy. The purpose of mammography prior to biopsy of a palpable abnormality is to find occult cancers, including multifocal carcinoma (see Fig. 13). On the basis of the newest evidence of the benefit of screening, the American Cancer Society, National Cancer Institute, and nine other research and medical associations joined to issue uniform mammography screening guidelines on June 27, 1989: 1 ,74 Age 40 and over: Annual clinical breast examination by a health professional; Age 40 to 49: Mammogram every 1 to 2 years; Age 50 and over: Mammogram annually. Important differences from the previous guidelines are the deletion of a recommendation for a baseline mammogram at age 35 and greater support for screening women ages 40 to 49.

UNDER UTILIZATION OF MAMMOGRAPHY The underutilization of mammography for breast cancer screening was noted as far back as 1955,42 and despite encouraging results from recent screening studies, mammography is still underutilized in the US. For example, in 1987, it was reported that only 15 to 20 per cent of American women over the age of 50 years had ever had a mammogram. 55 This information has stimulated investigators to identify the following barriers to mammographic screening: 1. Lack of awareness by patients of breast cancer screening guidelines and benefits'"; 2. Lack of awareness by physicians of breast cancer screening guidelines and benefits49 ; 3. Physician misperception of patient compliance, expecting undue worry, noncompliance, and outright rejection of any recommendation 26 ; 4. Physician concern about radiation risk", 26, 10\ 5. Physician concern about overdiagnosis and unnecessary biopsies 39 ; 6, Patient fear of discovering a lethal cancer and losing a breast69 ; 7, Perception that there will be great discomfort during the mammographic examination55 ; 8, High cost and low yield of the examination. 11, 104

A 1985 study of 257 Michigan women indicated that 53 to 69 per cent practiced breast self-examination, and 70 to 78 per cent were having regular clinical examinations. 38 However, only 34 per cent knew that an annual mammogram was recommended for women age 50 or older, and only 19 per cent of the women ages 35 to 49 and only 25 per cent of the women

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over 50 had ever had a mammogram. Of those who had, 46 per cent had had the study because of clinical findings; only 9 per cent had had it for health maintenance or cancer prevention; and 26 per cent had had a mammogram without knowing the specific reason. Less than 1 per cent obtained the mammograms because of media advertising or breast cancer in the family.39 Forty-eight per cent of the women said they would Have future mammograms based solely on the advice of their physician. A survey of attitudes and practices of primary care physicians conducted in 1984 found that only 49 per cent had ordered screening mammograms for asymptomatic women. 104 A 1987 National Cancer Institute Health Survey found that for women over 40, only 17 per cent had had mammograms in the past year, and only 37 per cent had ever had a mammogram. 74 Several studies show that a recommendation by a physician is the most compelling reason for a woman to have a mammogram. 39, 55 Thus, the physician plays an important role in promoting mammographic screening for breast cancer. OVERCOMING BARRIERS TO SCREENING Many of the barriers to screening can be overcome by educating physicians and patients about the value of screening mammography and by reducing its cost. Education· Physicians should know more about the many mammography screening studies that have resulted in a significant decrease in death from breast cancer. Some confusion has resulted from the inconsistent guidelines from one medical organization to another. The American Cancer Society and National Cancer Institute, among others, have attempted to reduce this confusion through their recent joint announcement of uniform guidelines. 74 Patients can be assured that the regular use of screening mammography may result in saving, not losing, a breast by detecting cancer at a stage when it can be treated conservatively. 34 Clinicians can now reassure patients that mammography is safe. 32 The American Cancer Society has stated that "modern technology has reduced the risk of radiation exposure of low-dose mammography to the point of negligible risk, if the risk exists at all, and has increased the diagnostic capabilities at the same time."53 One investigator has calculated that if 1 million women were to receive periodic screening mammograms beginning at age 40, two or three cancers might develop as a result of the radiation during a lifetime, whereas 70,000 breast cancers would occur naturally in these women. Thus, thousands of lives could be saved through early detection. 17 Discomfort from breast compression has been thought to be a deterrent. However, one recent study showed that compression was almost always acceptable to patients when they understood its importance. 56 Another recent survey of 1800 women found that 88 per cent experienced no or only mild discomfort, 1 per cent serious discomfort, and 1 per cent

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moderate pain. 102 No woman had pain so severe that it would make her reconsider having another mammogram. Physicians who fear excessive false-positive findings and unnecessary biopsies secondary to mammography screening should be aware that the number of cancers detected is directly correlated with the aggressiveness of the detection process. Nonetheless, the American College of Radiology encourages radiologists to monitor their biopsy results for mammographically detected lesions and to strive to attain an acceptable rate of truepositive results for their practice, probably in the range of one cancer per three to six biopsies. It also is important to realize that the true-positive biopsy rate for palpable lesions is likewise in the range of one cancer per three to six biopsies. Cost Reduction High cost has persisted as a barrier to breast cancer screening. 7, 104 A 1986 survey of 58 facilities in Los Angeles showed that the cost of a mammographic examination ranged from $50 to $205, with an average of $125.14 For the radiologist, the most effective way to decrease screening costs has been to differentiate diagnostic from screening examinations. 1 The diagnostic, or consultative, examination involves a complete customized evaluation of a symptomatic patient and often includes additional views of the abnormal breast, physical examination, and breast sonography. The screening examination is for an asymptomatic woman and is limited to two views of each breast; it should cost less to perform. An increasing number of facilities are offering a lower-priced screening examination. 14 In 1986, several regional offices of the American Cancer Society organized programs offering screening mammography for $50. The Society launched the "Breast Cancer Detection Awareness" campaign by designating April 1987 National Breast Cancer Awareness Month. Since then, many radiologists, hospitals, and volunteers throughout the nation have come together every year to provide low-cost screening as part of the Annual Cancer Crusade. Until recently, mammographic screening usually was not covered by health insurance, although a few health maintenance organizations such as Kaiser and CIGNA of California have supported mammographic screening and have followed the American Cancer Society guidelines. In the past, some clinicians and radiologists resorted to fabricating diagnoses such as "fibrocystic disease" to ensure reimbursement for their patients. Unfortunately, these practices sometimes backfired when patients were denied breast health insurance because of a "pre-existing condition."7 Public pressure for mandatory insurance coverage of mammographic breast cancer screening is increasing, and many legislative bills have been introduced mandating insurance coverage of screening mammography at both the state and federal level. As of July 1, 1989, 22 states had enacted legislation mandating insurance coverage of mammograms, 3 had laws supporting mammography screening and education, and legislation was pending in 14 other states. 112

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BREAST SONOGRAPHY (ULTRASOUND) Utility The breast was one of the first organs examined by ultrasound. 116 Although breast sonography has at various times been promoted for cancer screening,22, 61 its sensitivity and specificity in this application are far lower than those of mammography. 15, 63, 94 The limitations of ultrasound for screening include poor results with fatty breasts; inability to depict microcalcifications; inconsistent detection of solid lesions smaller than 1 cm; unreliable criteria for differentiating benign and malignant solid masses, resulting in a large number of unnecessary biopsies; and excessive scan time, reviewing time, and cost. Sonography has served more effectively as an adjunct to mammography to determine whether palpable or nonpalpable masses are cystic or solid and to evaluate the breast when dense parenchymal tissue limits the mammographic depiction of palpable abnormalities. 37, 75, 85, 108 Sonography may be useful for the examination and follow-up of breasts of young and pregnant women and of women with fibrocystic changes. 51 Breast sonography is most appropriate for differentiating cystic from solid masses found by palpation or on mammograms, with reported accuracy rates of 96 to 100 per cent. 36, 52, 58, 95 It is indispensable for cystic-solid differentiation of a nonpalpable, mammographically detected mass for which aspiration is likely to be unsuccessful. 36, 52, 58, 95 Ultrasound-guided needle aspiration and prebiopsy needle localization may be employed for nonpalpable sonographically detected lesions. 64 Sonographic Features of Breast Masses Sonography can detect cysts as small as 2 mm.58 The sonographic features of cysts include well-circumscribed anterior and posterior boundaries, round or oval shape, anechoic interior, and enhanced echoes distal to the lesion 52,58 (Fig. 14). Of these features, an anechoic interior is the most diagnostic. Fibroadenomas are the most frequent breast masses in women less than 25 years of age. The usual sonographic features include smooth, wellcircumscribed margins; round, oval, or lobulated shape; and weak, uniform echoes. 57 The sonographic features of carcinoma depend on its histologic type. Infiltrating ductal carcinomas have irregular, moderately sharp but uneven anterior margins but poorly seen or absent posterior margins, with echoes that may be attenuating distal to the lesion23 (Fig. 15). Internal echoes are inhomogeneous and weaker than those in the surrounding parenchyma. There often is a decrease in echoes distal to the tumor, which is believed to be secondary to the high absorption of sound by the tumor. As with mammography, 10 per cent of cancers depicted by ultrasound have well-circumscribed margins. These lesions tend to have sonographic features that mimic benign solid masses such as fibroadenomas: smooth margins with sharp anterior and posterior boundaries, homogeneous internal echoes, and a variable appearance of echoes posterior to the tumor.

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Figure 14. Sonogram of cyst. Bilobed anechoic mass (arrow) has sharp anterior and posterior borders. Echoes posterior to mass are increased in intensity (arrowheads) because of the low attenuation of sound through the fluid-filled cyst relative to the surrounding parenchymal tissue.

OTHER BREAST IMAGING TECHNIQUES

Diaphanography, also called transillumination or light scanning, was introduced more than 50 years ago. 27 After initial interest, it was not pursued further until the 1950s. Progress was made with the appreciation that breast cancer absorbs more near-infrared radiation than does benign tissue. Television cameras have been used to record the infrared radiation and display the image on a monitor using the visible-light spectrum. Despite these advances, diaphanography suffers from inability to show deep lesions or to detect small lesions. 76, 91 Thermography detects changes in breast temperature that may be indicative of abnormalities including carcinoma. Telethermography utilizes infrared radiation, liquid crystal thermography uses esters of cholesterol that change color in response to temperature changes, 78, III computerassisted thermography records discrete temperature measurements taken

Figure 15. Sonogram of carcinoma. Mass (arrow) has internal echoes indicating that it is solid. Its anterior boundary is irregular, and the posterior boundary is barely visible. Echoes posterior to the mass (arrowheads) are decreased in intensity because of its high attenuation of sound.

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at standardized locations,118 graphic stress telethermography compares temperature readings taken before and after immersion of the hand in ice water,l00 and microwave thermography uses radiation of longer wavelengths. 5 Despite 33 years of investigation of thermography for the detection of breast cancer, its use continues to be controversial. llo Most small, non palpable lesions do not demonstrate increased heat, and most women with more heat in one breast than the other have no cancer. The American College of Radiology maintains that the use of modalities such as ultrasonography, diaphanography, and thermography in screening is not cost effective and should not be part of the basic screening process. 2 Magnetic resonance imaging (MRI) of the breast is a newer imaging method on which only a few published reports have appeared. Thus far, considerable overlap in the MRI features of malignant and benign lesions has been observed. 84 Also, the high cost of MRI and its inability to resolve smaller masses and microcalcifications make it impractical for breast imaging at this time.

SUMMARY Breast radiography should be performed only with film-screen mammography or xeromammography. At least two views of each breast should be obtained, and for film-screen mammography, at least one of these should be the oblique view. Quality assurance is becoming a significant concern in breast cancer screening. The ACR Mammography Accreditation Program takes into account the qualifications of the personnel, the performance of the x-ray equipment, and a peer review of the final product: the diagnostic image. The mammographic signs of malignancy can be divided into primary, secondary, and indirect. The accuracy of mammography depends on several factors, but the greatest limitation is the density of the breast tissue. Very dense tissue makes detection of breast cancer difficult, and a negative mammogram should never deter one from a biopsy of a clinically suspect mass. New consensus guidelines for breast cancer screening were developed to bring uniformity to the recommendations of the American Cancer Society, the National Cancer Institute, and various professional medical societies. These new guidelines reflect the encouraging results from recent clinical trials, as well as some discouraging reports on breast self-examination and the baseline mammogram. The underutilization of screening mammography is a problem of significant concern to both private and public health agencies. Barriers to mammographic screening include lack of awareness of the benefits of screening, physicians' misconceptions about patient compliance, concerns about radiation risk and overdiagnosis, fear of mastectomy, a perception that a mammogram involves great discomfort, and relatively high cost. Nationwide educational programs are under way to counter misconceptions about mammography, and various strategies are evolving to overcome the other barriers. Sonography is a useful adjunct to mam-

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mography for cyst-solid differentiation, but mammography is the only imaging modality effective for the early detection of breast cancer.

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