Troubleshooting to Overcome Technical Challenges in Image-guided Breast Biopsy.

Image-guided breast biopsy with stereotactic, ultrasonographic, or magnetic resonance imaging guidance has become an integral component of every breast imaging program. It has many advantages over open surgical biopsy, including lower cost, lower patient morbidity, faster patient recovery, and minimal to no scarring, with equal accuracy to that of open surgical biopsy. Successful completion of a breast biopsy begins with thorough preprocedural planning to choose the appropriate imaging modality and most efficient biopsy approach. Patient mental and physical comorbidities, anticoagulation status, small or thin breasts, and breast implants, as well as lesion conspicuity and posterior, superficial, axillary, or subareolar location, pose technical challenges to successful image-guided breast biopsy that must be overcome. When biopsy is performed with use of a different imaging modality than that used to initially identify the target, careful preprocedural multimodality radiologic correlation, postprocedural identification of the biopsy marker location, and radiologic-pathologic correlation must be undertaken to ensure accurate biopsy of the intended target with use of the different modality. If, after employing all available strategic and procedural modifications, image-guided breast biopsy cannot be performed, then surgical excision of the intended target should be recommended at the time of biopsy cancellation to avoid a delay in diagnosis. This article reviews patient and lesion factors that pose technical challenges to successful breast biopsy and presents strategies and procedural modifications that aid in successful completion of breast biopsy in challenging situations. ©RSNA, 2017.

Clinical Utility of Breast MRI in the Diagnosis of Malignancy After Inconclusive or Equivocal Mammographic Diagnostic Evaluation.

OBJECTIVE: The purpose of this study was to determine the clinical utility of breast MRI for diagnosing malignancy in women with equivocal mammographic findings but no symptoms. MATERIALS AND METHODS: Retrospective review of an institutional MRI database of 7332 contrast-enhanced breast MRI examinations from January 1, 2009, through December 31, 2012, yielded the records of 296 (4.0%) examinations of 294 women without symptoms who underwent MRI for mammographic findings uncertain at diagnostic evaluation. Imaging findings, histopathologic results, and patient demographics were obtained from the electronic medical record. RESULTS: The mean patient age was 55 years (range, 29-83 years). Mammographic lesion type (n = 294) included 89 focal asymmetries, 76 asymmetries, 64 masses, 44 architectural distortions, 17 surgical scar versus lesion, and four miscellaneous lesions. Diagnostic ultrasound, performed on 286 of 294 (97.3%) lesions at mammographic evaluation, showed an ultrasound correlate in 37 (12.9%) lesions, equivocal correlate in 48 (16.8%), and no ultrasound correlate in 201 (70.3%). MRI examination of 294 index lesions showed a correlate in 133 (45.2%) and no correlate in 161 (54.8%). Forty of 294 (13.6%) index lesions were malignant, 37 (92.5%) with an MRI correlate and three (7.5%) without an MRI correlate. Among 250 patients who underwent biopsy or had 2 or more years of imaging stability, the sensitivity, specificity, negative predictive value, and positive predictive value of breast MRI for malignancy were 92.5%, 62.4%, 97.8%, and 31.9%. Forty-four of 294 (15.0%) patients had lesions incidentally found at MRI; 7 of 41 (17.1%) lesions that were biopsied or were stable for at least 1 year were malignant. CONCLUSION: Problem-solving breast MRI for inconclusive mammographic findings helps identify malignancies with high sensitivity and a high negative predictive value.

Avoiding Pitfalls, Maximizing Success at Image-guided Breast Interventions: A Pictorial Review.

Imaging and image-guided interventions have become increasingly important in the workup and treatment of breast lesions in the past 2 decades. Radiologists should be aware of potential pitfalls during the workup, the procedure itself, and in the postprocedure follow-up. In this pictorial review, we illustrate challenges related to technique and interpretation related to breast interventions, and suggest ways to maximize success.

Imaging and Histopathologic Features of BI-RADS 3 Lesions Upgraded during Imaging Surveillance.

To evaluate imaging and histopathologic differences between screen-detected benign and malignant upgraded lesions initially assessed as BI-RADS 3 at diagnostic evaluation. An IRB approved retrospective review of the mammography data base from January 1, 2004 to December 31, 2008 identified 1,188 (1.07%) of 110,776 screening examinations assessed as BI-RADS 3 following diagnostic evaluation at our academic center (staffed by breast specialists) or our outpatient center (staffed by general radiologists), 1,017 with at least 24 months follow-up or biopsy. Sixty (5.9%) BI-RADS 3 lesions were upgraded to BI-RADS 4 or 5 during imaging surveillance (study population). Prospective reports, patient demographics, and clinical outcomes were abstracted from the longitudinal medical record. Mean patient age was 54.1 years (range 35-85). Lesions consisted of 7 masses, 12 focal asymmetries and 41 calcifications. Fifteen (25%) of 60 lesions upgraded from initial BI-RADS 3 assessment were malignant (1.47% of total; 15/1,017 BI-RADS 3 studies). Malignancy rates by upgraded lesion type showed no significant difference: Thirty-three (73.3%) of 45 benign upgraded lesions were calcifications compared to 8 (53.3%) of 15 malignant upgraded lesions (p = 0.202). Twelve (26.7%) of 45 benign upgraded lesions were masses or focal asymmetries, compared to 7 (46.7%) of 15 upgraded malignant lesions (p = 0.202). Six (85.7%) of 7 malignant upgraded masses/focal asymmetries had no US correlate at initial BI-RADS 3 assessment compared to 7 (58.3%) of 12 benign upgraded masses/focal asymmetries (p = 0.33). Breast-imaging specialists interpreted 21 studies, 3 (14.3%) malignant; general radiologists interpreted 39 studies, 12 (30.8%) malignant (p = 0.218). There was no significant difference in malignancy rate among different types of upgraded mammographic lesions, nor depending on subspecialty interpretation versus nonsubspecialist interpretation. Although calcifications made up a majority of upgraded lesions, most were benign, suggesting that decreased surveillance of calcifications may be appropriate.

Assessment and Management of Challenging BI-RADS Category 3 Mammographic Lesions.

Breast Imaging Reporting and Data System (BI-RADS) category 3 lesions are probably benign by definition and are recommended for short-interval follow-up after a diagnostic workup has been completed. Although the original lexicon-derived BI-RADS category 3 definition applied to lesions without prior imaging studies (when stability could not be determined), in clinical practice, many lesions with prior images may be assigned to BI-RADS category 3. Although the BI-RADS fifth edition specifically delineates lesions that are appropriate for categorization as probably benign, it also specifies that the interpreting radiologist may use his or her discretion and experience to justify a "watchful waiting" approach for lesions that do not meet established criteria. Examples of such lesions include evolving masses or calcifications suggestive of prior trauma and instances when stability cannot be ascertained because of image quality. Although interval change is an important feature of malignancy, many benign lesions also change over time; thus, use of prior imaging studies and ongoing imaging surveillance to demonstrate the evolution of a probably benign lesion is justified. Some examples of common pitfalls associated with inappropriate BI-RADS category 3 assessment include failure to use proper BI-RADS descriptors, failure to perform a complete diagnostic workup, and overreliance on negative ultrasonographic findings. When appropriately used, short-interval follow-up saves many patients from undergoing biopsy of benign lesions, without decreasing the rate of cancer detection. (©)RSNA, 2016.

Breast MR Imaging for Equivocal Mammographic Findings: Help or Hindrance?

Breast magnetic resonance (MR) imaging, because of its extremely high sensitivity in detecting invasive breast cancers, is sometimes used as a diagnostic tool to evaluate equivocal mammographic findings. However, breast MR imaging should never substitute for a complete diagnostic evaluation or for biopsy of suspected, localizable suspicious mammographic lesions, whenever possible. The modality's high cost, in addition to only moderate specificity, mandate that radiologists use it sparingly and with discrimination for problematic mammographic findings. It is rare that the reality or significance of a noncalcified mammographic finding remains equivocal or problematic at diagnostic mammography evaluation, which usually includes targeted ultrasonography (US). There are several reasons for this infrequent occurrence: (a) an asymmetry may persist on diagnostic views but be visible only on craniocaudal or mediolateral oblique projections, precluding three-dimensional localization for US or biopsy, or a lesion may persist on some diagnostic spot views but dissipate or efface on others; (b) uncertainty may exist as to whether apparent change is clinically important or owing to technical factors such as compression or positioning differences; or (c) a lesion may be suspected but biopsy options are limited owing to lack of a US correlate and lesion inaccessibility for stereotactic biopsy, or biopsy of a vague or questionably real lesion has been attempted unsuccessfully. This article will discuss the indications for problem-solving MR imaging for equivocal mammographic findings, present cases illustrating appropriate and inappropriate uses of problem-solving MR imaging, and present false-positive and false-negative cases affecting the specificity of breast MR imaging. (©)RSNA, 2016.

Characteristics, Malignancy Rate, and Follow-up of BI-RADS Category 3 Lesions Identified at Breast MR Imaging: Implications for MR Image Interpretation and Management.

Purpose To (a) evaluate the frequency of Breast Imaging Reporting and Data System (BI-RADS) category 3 assessment in screening and diagnostic breast magnetic resonance (MR) imaging, (b) review findings considered indicative of BI-RADS category 3, and (c) determine outcomes of BI-RADS category 3 lesions, including upgrades, downgrades, and malignancy rates. Materials and Methods This retrospective study was approved by the institutional review board and compliant with HIPAA. The authors retrospectively reviewed the breast MR imaging database (2009-2011) to identify breast MR images classified as showing BI-RADS category 3 lesions. There were 9216 BI-RADS assessments in 5778 examinations (3360 women). Of the 9216 assessments, 567 (6%) in 483 women (average age, 47.2 years; median age, 47.0 years) were assigned BI-RADS category 3. In women with more than one BI-RADS category 3 lesion, the first lesion reported in the impression was used for data analysis. Outcomes data were available for 435 of the 483 women (90.1%). These women comprised the study cohort. Medical records from January 1, 2009, to May 31, 2015, were reviewed to obtain demographic characteristics and outcomes. χ(2) statistics and 95% exact confidence intervals (CIs) were constructed. Results MR imaging was performed for high-risk screening in 240 of the 435 patients (55.2%) and for diagnostic purposes in 195 (44.8%). Findings included mass (n = 125, 28.7%), focus (n = 111, 25.5%), nonmass enhancement (n = 80, 18.3%), moderate or marked background parenchymal enhancement (BPE) (n = 91, 20.9%), posttreatment changes (n = 16, 3.8%), and other findings (n = 12, 2.8%). Outcomes were as follows: 339 of the 435 patients (78%) did not have evidence of malignancy at more than 24 months, 28 (6.4%) underwent mastectomy (all benign), and 68 (15.6%) had lesion upgrades, with 11 cancers (2.5%). All 11 cancers were diagnosed in women with a genetic mutation or a personal history of breast cancer. No cancer was detected in cases of moderate or marked BPE. Conclusion Six percent of all breast MR imaging assessments were categorized as BI-RADS category 3, with a cancer rate of 2.5% (95% CI: 1.3%, 4.5%). All cancers were in women with a genetic mutation or personal history of breast cancer. Marked BPE does not necessitate a BI-RADS 3 assessment. (©) RSNA, 2016.

Effect of Training on Qualitative Mammographic Density Assessment.

PURPOSE: The aim of this study was to evaluate the accuracy of visual mammographic breast density assessment and determine if training can improve this assessment, to compare the accuracy of qualitative density assessment before and after training with a quantitative assessment tool, and to evaluate agreement between qualitative and quantitative density assessment methods. METHODS: Consecutive screening mammograms performed over a 4-month period were visually assessed by two study breast radiologists (the leads), who selected 200 cases equally distributed among the four BI-RADS density categories. These 200 cases were shown to 20 other breast radiologists (the readers) before and after viewing a training module on visual density assessment. Agreement between reader assessment and lead radiologist assessment was calculated for both reading sessions. Quantitative volumetric density of the 200 mammograms, determined using a commercially available tool, was compared with both sets of reader assessment and with lead radiologist assessment. RESULTS: Compared with lead radiologist assessment, reader accuracy of breast density assessment increased from 65% before training to 72% after training (odds ratio, 1.41; P < .0001). Training specifically improved assignment to BI-RADS categories 1 (P < .0001) and 4 (P < .10). Compared with quantitative assessment, reader accuracy showed statistically nonsignificant improvement with training (odds ratio, 1.1; P = .26). Substantial agreement between qualitative and quantitative breast density assessment was demonstrated (κ = 0.78). CONCLUSIONS: Training may improve the accuracy of mammographic breast density assessment. Substantial agreement between qualitative and quantitative breast density assessment exists.

The Breast Imager's Approach to Nonmammary Masses at Breast and Axillary US: Imaging Technique, Clues to Origin, and Management.

Ultrasonography (US) of the breast and axilla is primarily used to evaluate a symptomatic patient or to further investigate findings identified with other imaging modalities. Breast imagers are generally familiar with US evaluation of level I, II, and III axillary lymph nodes in the diagnosis and staging of breast cancer. However, the axilla contains nonlymphatic tissue as well, including muscle, fat, and vascular and neurologic structures, and anatomically the breast lies on the chest wall. Therefore, lesions of nonmammary and non-lymph node origin in the axilla or chest wall are not infrequently encountered during US evaluation of the breast or axilla. In fact, such lesions may be the reason that the patient presents to the breast imaging department for evaluation. Understanding the anatomy of the chest wall and axilla and using a systematic US approach will help radiologists expedite accurate diagnosis, suggest optimal additional imaging, and streamline appropriate clinical referral. Key imaging features of nonmammary non-lymph node masses are highlighted, and case examples are provided to illustrate these features. Appropriate patient management is critical in these cases because referral to a breast surgeon may not be the best next step. Depending on institutional referral patterns, other subspecialty surgeons will be involved. Online supplemental material is available for this article.

Developing Asymmetry at Mammography: Correlation with US and MR Imaging and Histopathologic Findings.

PURPOSE: To evaluate ultrasonographic (US) and magnetic resonance (MR) imaging findings, histopathologic etiologies, and outcomes for developing asymmetry at mammography. MATERIALS AND METHODS: In this institutional review board-approved, informed consent-waived, HIPAA-compliant, retrospective review of a mammography database for records from January 1, 2009 to December 31, 2012, 2354 consecutive diagnostic mammograms classified as showing focal asymmetry were identified. After patients with benign results, those considered stable, and those without prior mammograms were excluded, images from 521 studies were reviewed and 202 developing lesions were identified in 201 women. Patient demographics, US and MR imaging findings, and clinical and histopathologic outcomes were obtained from the electronic medical records. Equivocal US correlates of findings with developing asymmetry detected at mammography were excluded from statistical analysis. The Fisher exact test and Student t test analysis were performed and relative risk and 95% confidence intervals (CIs) were determined. RESULTS: Biopsy was performed in 73 (36%) of 201 patients with developing asymmetries, with 42 (58%) benign and 31 (42%) malignant results. Of 128 patients with nonbiopsied lesions, 110 (86%) were stable at 24 months (considered benign), 12 (9.4%) were stable at less than 24 months, and six (4.7%) were lost to follow-up. Diagnostic US was performed in 186 (93%) of 201 patients, 74 (40%) with correlates. US was performed in 30 (97%) of 31 patients with malignant developing asymmetries, 17 (57%) with correlates, and in 140 (92%) of 152 patients with benign lesions, 51 (36%) with correlates (risk ratio, 1.92; 95% CI: 1.001, 3.695; two-tailed P = .064, one-tailed P = .038). MR imaging was performed in 66 (33%) of 201 patients, 26 (39%) with correlates. MR imaging was performed in 10 (32%) of 31 patients with malignant developing asymmetries, all with correlates, and 53 (35%) of 152 patients with benign lesions, 15 (28%) with correlates (P < .0001). CONCLUSION: Developing asymmetries were malignant in 15% (95% CI: 11%, 21.1%) of patients. Presence of a US or MR imaging correlate was predictive of malignancy.

Patient and Provider Perspectives on Mammographic Breast Density Notification Legislation.

Background: Patient advocacy has fostered the implementation of mammographic breast density (MBD) notification legislation in many states. Little is known about the perspectives of women, primary care physicians (PCPs), and breast radiologists in response to this legislation. The objective of this research was to elicit qualitative information from these multiple stakeholders to understand varied perspectives on the subject of MBD notification and inform best practices around implementation. Methods: Content analysis of narrative data from focus groups with women (2 groups, total of 16 participants) and in-depth interviews with PCPs (n = 7) and breast radiologists (n = 7). Results: Three major themes emerged from the data: 1) knowledge and general attitudes about legislation, 2) concerns about consequences, and 3) actions patients and clinicians should consider based on MBD information. For each of these themes, the views of women, PCPs, and radiologists often demonstrated different perspectives. Conclusion: This work supports the need for clear and concise tools for patients and providers to understand MBD in the context of a woman's overall breast cancer risk with guidance on next steps.

Breast cancer screening in the era of density notification legislation: summary of 2014 Massachusetts experience and suggestion of an evidence-based management algorithm by multi-disciplinary expert panel.

Stemming from breast density notification legislation in Massachusetts effective 2015, we sought to develop a collaborative evidence-based approach to density notification that could be used by practitioners across the state. Our goal was to develop an evidence-based consensus management algorithm to help patients and health care providers follow best practices to implement a coordinated, evidence-based, cost-effective, sustainable practice and to standardize care in recommendations for supplemental screening. We formed the Massachusetts Breast Risk Education and Assessment Task Force (MA-BREAST) a multi-institutional, multi-disciplinary panel of expert radiologists, surgeons, primary care physicians, and oncologists to develop a collaborative approach to density notification legislation. Using evidence-based data from the Institute for Clinical and Economic Review, the Cochrane review, National Comprehensive Cancer Network guidelines, American Cancer Society recommendations, and American College of Radiology appropriateness criteria, the group collaboratively developed an evidence-based best-practices algorithm. The expert consensus algorithm uses breast density as one element in the risk stratification to determine the need for supplemental screening. Women with dense breasts and otherwise low risk (<15% lifetime risk), do not routinely require supplemental screening per the expert consensus. Women of high risk (>20% lifetime) should consider supplemental screening MRI in addition to routine mammography regardless of breast density. We report the development of the multi-disciplinary collaborative approach to density notification. We propose a risk stratification algorithm to assess personal level of risk to determine the need for supplemental screening for an individual woman.

Screening Breast MRI in Patients Previously Treated for Breast Cancer: Diagnostic Yield for Cancer and Abnormal Interpretation Rate.

RATIONALE AND OBJECTIVES: To determine the cancer detection rate and abnormal interpretation rate of screening breast magnetic resonance imaging (MRI) in previously treated breast cancer patients. MATERIALS AND METHODS: Institutional review board-approved retrospective review of the breast MRI database from 2009 to 2011 identified a total of 3297 screening examinations. After excluding genetic mutation carriers, untested first-degree relatives of known mutation carriers, and patients with a history of chest irradiation, there were 1194 (36.2%) examinations in 691 patients previously treated for breast cancer. MRI reports were reviewed to determine MRI findings and breast imaging reporting and data system (BI-RADS) assessments. The longitudinal medical record was reviewed to determine patient demographics and outcomes of imaging surveillance and biopsy. RESULTS: Mean patient age at initial cancer diagnosis was 46.1 years, and mean patient age during the study interval was 52 years. Cancer detection rate was 10 per 1000 (1%; 95% confidence interval [CI], 0.5%-1.8%]; 12 of 1194 examinations). Overall 10.7% (128 of 1194) of examinations received an abnormal interpretation, including 5.4% (65 of 1194) BI-RADS 4 or 5 and 5.3% (63 of 1194) BI-RADS 3 assessments with a 9.4% positive predictive value (PPV1; 12 of 128 examinations) and a 17.9% PPV3 (12 malignancies per 67 biopsies). CONCLUSIONS: Screening breast MRI in women previously treated for breast cancer detected cancer in 1.0% of examinations, with a 10.7% abnormal interpretation rate, and a PPV for malignancy of 17.9%.

The Influence of Radiology Image Consultation in the Surgical Management of Breast Cancer Patients.

BACKGROUND: Patients referred to comprehensive cancer centers arrive with clinical data requiring review. Radiology consultation for second opinions often generates additional imaging requests; however, the impact of this service on breast cancer management remains unclear. We sought to identify the incidence of additional imaging requests and the effect additional imaging has on patients' ultimate surgical management. METHODS: Between November 2013 and March 2014, 153 consecutive patients with breast cancer received second opinion imaging reviews and definitive surgery at our cancer center. We identified the number of additional imaging requests, the number of fulfilled requests, the modality of additional imaging completed, the number of biopsies performed, and the number of patients whose management was altered due to additional imaging results. RESULTS: Of 153 patients, the mean age was 55 years; 98.9% were female; 23.5% (36) had in situ carcinoma (35 DCIS/1 LCIS), and 76.5% (117) had invasive carcinoma. Additional imaging was suggested for 47.7% (73/153) of patients. After multidisciplinary consultation, 65.8% (48/73) of patients underwent additional imaging. Imaging review resulted in biopsy in 43.7% (21/48) of patients and ultimately altered preliminary treatment plans in 37.5% (18/48) of patients (Fig. 1). Changes in management included: conversion to mastectomy or breast conservation, neoadjuvant therapy, additional wire placement, and need for contralateral breast surgery. Fig. 1 Impact of second-opinion imaging reviews on the management of breast cancer patients CONCLUSIONS: Our analysis of second opinion imaging consultation demonstrates the significant value that this service has on breast cancer management. Overall, 11.7% (18/153) of patients who underwent breast surgery had management changes as a consequence of radiologic imaging review.

Breast density: clinical implications and assessment methods.

Breast density assessment is an important component of the screening mammography report and conveys information to referring clinicians about mammographic sensitivity and the relative risk for developing breast cancer. These topics have gained substantial attention because of recent legislation in several states that requires patients to be informed of dense breast tissue and the potential for associated breast cancer risk and decreased mammographic sensitivity. Because of the considerable implications of diagnosing a woman with dense breast tissue, radiologists should strive to be as consistent as possible when assessing breast density. Commonly used methods of breast density assessment range from subjective visual estimation to quantitative calculations of area and volume density percentages made with complex computer algorithms. The basic principles of currently available commercial methods of calculating fibroglandular density are described and illustrated. There is no criterion standard for determining breast density, but understanding the pros and cons of the various assessment methods will allow radiologists to make informed decisions. Radiologists should understand the basic factors involved in breast density assessment, the changes related to density assessment described in the fifth edition of the American College of Radiology Breast Imaging Reporting and Data System (BI-RADS) lexicon, and the capabilities of currently available software. Online supplemental material is available for this article.

Older women's experience with a benign breast biopsy­a mixed methods study.

BACKGROUND: Little is known about older women's experience with a benign breast biopsy. OBJECTIVES: To examine the psychological impact and experience of women ≥ 65 years of age with a benign breast biopsy. DESIGN: Prospective cohort study using quantitative and qualitative methods. SETTING: Three Boston-based breast imaging centers. PARTICIPANTS: Ninety-four English-speaking women ≥ 65 years without dementia referred for breast biopsy as a result of an abnormal mammogram, not aware of their biopsy results at baseline, and with a subsequent negative biopsy. MEASUREMENTS: We interviewed women at the time of breast biopsy (before women knew their results) and 6 months post-biopsy. At both interviews, participants completed the validated negative psychological consequences of screening mammography questionnaire (PCQ, scores range from 0 to 36 [high distress], PCQ ≥ 1 suggests a psychological consequence, PCQs <1 are reported at time of screening) and women responded to open-ended questions about their experience. At follow-up, participants described the quality of information received after their benign breast biopsy. We used a linear mixed effects model to examine if PCQs declined over time. We also reviewed participants' open-ended comments for themes. RESULTS: Overall, 88% (83/94) of participants were non-Hispanic white and 33% (31/94) had a high-school degree or less. At biopsy, 76% (71/94) reported negative psychological consequences from their biopsy compared to 39% (37/94) at follow-up (p < 0.01). In open-ended comments, participants noted the anxiety (29%, 27/94) and discomfort (28%, 26/94) experienced at biopsy (especially from positioning on the biopsy table). Participants requested more information to prepare for a biopsy and to interpret their negative results. Forty-four percent (39/89) reported at least a little anxiety about future mammograms. CONCLUSIONS: The high psychological burden of a benign breast biopsy among older women significantly diminishes with time but does not completely resolve. To reduce this burden, older women need more information about undergoing a breast biopsy.

Interpreting one-view mammographic findings: minimizing callbacks while maximizing cancer detection.

Overlap of breast tissue is a frequent consequence of the necessary positioning and compression of the three-dimensional breast to obtain two-dimensional mammograms. The mammary glands contain fewer anatomically fixed landmarks than solid organs do; thus, variability in positioning can have an even greater effect on mammography than it has on other imaging examinations. Most often, areas of overlapping fibroglandular tissue, also known as summation shadows, are seen on only one of the two standard mammographic views. While striving to detect breast cancer as early as possible, radiologists must learn to visually compensate for apparent abnormalities in the breast that are produced by such tissue overlap. Mammographic interpretation in this setting is made even more challenging by the fact that the only manifestation of breast cancer might be a subtle change on a single mammographic view. Breast cancer might be obscured on one of the two standard views because of the density of surrounding breast tissue, mammographic technique, lesion size or location within the breast, histopathologic characteristics of the tumor, or lack of effect by the tumor on the appearance of surrounding tissues. To heighten awareness of the factors that can lead to either unnecessary recalls or failure to identify breast cancer, cases are reviewed in which false-positive findings and breast cancers were visible on only one mammographic view. Strategies for interpreting screening mammograms and determining which findings merit diagnostic evaluation are outlined so as to help minimize false-positive findings and aid in cancer detection.