Breast Cancer Screening: An Evidence-Based Update

Synopsis

Routine screening mammography is recommended by most groups issuing breast cancer screening guidelines, especially for women ≥ 50 years of age. However, both the potential benefits and risks of screening should be discussed with individual patients to allow for shared decision-making regarding their participation in screening, age of commencement and conclusion, and interval of mammography screening.

Introduction

Breast cancer screening is used to identify women with asymptomatic cancer with the goal of enabling women to undergo less invasive treatments that lead to better outcomes, ideally at earlier stages before the cancer progresses. There are important considerations for who should be screened, how often women should be screened, and with which imaging modality (or modalities). Ultimately, clinicians need to help women understand the benefits and risks of breast cancer screening in order to make informed decisions.

Who should be screened?

Guidelines for who should undergo breast cancer screening vary within and among countries.¹ In the United States, the U.S. Preventive Services Task Force recommends that breast cancer screening with mammography be offered to women 50 to 74 years of age and that starting screening before age 50 years should be based on the individual woman's context, including her values regarding the benefits and risks.² The American Cancer Society recommends screening starting at age 40.³ Screening women 40 to 49 years of age is more controversial than older ages, with less evidence available to determine the risk-benefit balance. Analyses using six different breast cancer simulation models of the National Cancer Institute-funded Cancer Intervention and Surveillance Modeling Network (CISNET) found that starting biennial (every two years) screening at age 40 years with mammography, in comparison to age 50 years, was associated with reduced breast cancer mortality by an additional 3%, but at the expense of more false-positives and health care resources.⁴

There is little evidence to support screening women of average risk < 40 years of age. These women have a lower incidence of breast cancer and were largely excluded from randomized controlled trials (RCTs) involving screening mammography. Similarly, there is little evidence regarding screening women more than 75 years of age, as older women were also largely excluded from RCTs. Moreover, elderly women are more likely to have co-morbid medical conditions and may experience less marginal benefit from screening. It is not recommended that people with limited life expectancy (< 5 years) undergo routine screening, as early breast cancer detection and treatment could impair quality of life while not improving survival. However, women with limited life expectancy continue to be screened for breast cancer in the U.S.⁵

How often should women be screened?

Countries vary in how often they recommend women undergo breast cancer screening. In a prospective cohort study of U.S. women, it was found that after 10 years of screening with mammography, the cumulative probability of a woman receiving a false positive recall (of being called back for additional examination after abnormal screening but subsequently found to not have cancer) was lower with biennial screening than with annual screening.⁶ In addition, analyses using six CISNET simulation models found that biennial screening mammography maintained most of the benefit of annual screening while reducing false positive results by almost half.⁴ The United States Preventive Services Task Force, thus, currently recommends that women without additional risk factors undergo screening mammography biennially starting at age 50.

Methods of breast cancer screening

Breast cancer screening modalities include both physical breast exams as well as mammographic imaging. Additional supplemental screening with breast MRI may be considered for special high-risk populations.

Physical Examination

Breast self-examination

Many awareness campaigns encourage women to conduct monthly breast self-examinations. However, the evidence for mortality reduction from breast self-examination is limited. This topic has been investigated in randomized controlled trials, case-control studies, nonrandomized trials, and cohort studies.⁷ While self-examination may lead to detection of lesions at a smaller size, increased false positives and more testing have been noted with no reduction in mortality. Breast self-exam is no longer recommended by most guidelines.

Clinical breast examination

Clinical breast examination by a health care provider has been studied as a screening method used in conjunction with mammography. In the Canadian National Breast Screening Study of women age 50 to 59 years receiving either mammography and clinical breast examination or only clinical breast examination, the 25 year cumulative mortality from breast cancer diagnosed during the screening period was essentially equivalent between women who received mammography and clinical breast examination versus women who received only clinical breast examination.⁸ Of note, the clinical breast exams were performed by well-trained clinicians, the quality of the clinical breast exams were periodically evaluated, and the clinicians spent 5-10 minutes examining each breast.⁹ Community clinicians may not perform such high quality clinical breast exams, limiting the applicability of these results to general practice.

Imaging

Sample images of a right breast cancer screen-detected by full-field digital mammography and then seen on magnetic resonance imaging and ultrasound are included in Figure 2.

Figure 2.

Invasive cancer as seen by the following modalities: (a) screening mammogram, (b) ultrasound, and (c) MRI.

Screen-film mammography

Historically, screen-film mammography had been the standard method of breast cancer screening. In screen-film mammography, images were developed and fixed chemically, a process similar to film photography. Processing errors led to > 20 percent of images being rejected,¹⁰ resulting in repeat imaging which increased examination time, exposure to ionizing radiation, and costs. In the U.S., screen-film mammography has now largely been replaced by full-field digital mammography.

Full-field digital mammography

In full-field digital mammography, images are immediately displayed on a computer monitor for interpretation, enabling more rapid interpretation than with screen-film mammography.¹¹ The digital display also enables the use of computer-aided detection (CAD) software, which recognizes suspicious image patterns to aid in cancer detection. Full-field digital mammography has been shown to have higher contrast, lower noise, and greater dynamic range than screen-film mammography.¹²

Several clinical trials have found full-field digital mammography to be of similar or greater accuracy than screen-film mammography.^13-15 The Digital Mammography Imaging Screening Trial (DMIST) found full-field digital mammography to be of similar accuracy to screen-film mammography overall and of greater accuracy than screen-film mammography for three subpopulations: women < 50 years of age, pre- or peri-menopausal women, and women with mammographically dense breast tissue.¹⁶ Given this evidence and the other benefits of full-field digital mammography, including ease of storage and retrieval of images, full-field digital mammography has been progressively adopted as the modality of choice for breast cancer screening in the U.S.¹⁷ and now accounts for > 95% of all functioning mammography units in the U.S.¹⁸

Computer-Aided Detection

Computer-aided detection (CAD) software highlights potentially abnormal image features for radiologists. Early reports suggested that CAD was associated with improved detection of malignancies when used with either screen-film mammography or full-field digital mammography.^19,20 However, other reports suggest that CAD results in a significantly higher rate of false positives, as the programs usually add two to five marks per screening case on typical screening exams.^19,21-23 In addition, CAD's effect on patient outcomes (e.g., mortality) is currently uncertain. CAD has been found to increase detection of ductal carcinoma in situ (DCIS) and, in women without breast cancer, is associated with increased diagnostic testing after screening.²⁴ Results have been mixed regarding the effect of CAD on the stage at which invasive breast cancer is detected.^24,25 Despite such uncertainty and lack of data on outcomes, CAD is widely used with screening mammography.²⁶

Digital Breast Tomosynthesis

With digital breast tomosynthesis, a rotating gantry takes images of the breast from various angles in order to create a three-dimensional view.²⁷ This FDA-approved technology is now a standard feature in newer digital mammography units and rapidly diffusing into U.S. community practice.²⁸ The radiation dose from digital breast tomosynthesis equals the dose from routine mammography; thus, combined full-field digital mammography and digital breast tomosynthesis currently doubles the radiation dose at screening.²⁹ In May 2013, however, the FDA approved software allowing the reconstruction of the standard two-dimensional mammography image from the three-dimensional tomosynthesis acquisition, negating the doubling of radiation dose.

In two-dimensional full-field digital mammography, fibroglandular tissue directly above or below tumors can mask them, reducing sensitivity. Digital breast tomosynthesis's three-dimensional views enable radiologists to go through breast tissue slice by slice, reducing this masking effect. Two population-based screening studies in Europe and one large retrospective study in the U.S. have shown significantly increased cancer detection rates and decreased false-positive recall rates when digital breast tomosynthesis is added to full-field digital mammography.^30-32 Digital breast tomosynthesis may therefore reduce both patient morbidity and medical costs by reducing unnecessary diagnostic workups. In addition, digital breast tomosynthesis is less expensive and easier to use than other supplemental breast imaging tests such as screening ultrasound and screening MRI.²⁸

Magnetic Resonance Imaging and Ultrasound

Magnetic resonance imaging (MRI) and ultrasound are useful tools for evaluating abnormalities and diagnosing breast cancer, but they are not recommended as screening modalities for the general population. No studies have shown a mortality benefit for the general population from these imaging modalities. However, there may be mortality benefit for using MRI or ultrasound for supplemental screening in special very high-risk populations such as women with BRCA1 and BRCA2 mutations (see below).

Digital Infrared Thermal Imaging

A number of emerging imaging technologies are being developed for breast cancer screening and diagnosis. One that is gaining popularity is digital infrared thermal imaging or breast thermography, which aims to detect malignancy by identifying higher local skin temperature due to increased vascularization and inflammation caused by a developing malignancy.³³ Unfortunately, a recent systematic review concluded that there is currently insufficient evidence to recommend the use of this technology for breast cancer screening, with significant heterogeneity identified in published studies for both digital infrared thermal imaging's sensitivity (0.25-0.97) and specificity (0.12-0.85).³⁴

Special Populations

Dense breasts

Dense breast tissue reduces screening mammography's sensitivity to detect breast cancer,³⁵ and women with dense breasts have three to five times greater lifetime risk of developing breast cancer than women with mostly fatty breasts,^36-38 regardless of other risk factors.³⁹ Breast density falls along a spectrum from almost entirely fat, to scattered fibroglandular densities, to heterogeneously dense, to extremely dense (Figure 1). As of September 2014, 19 U.S. states (AL, AZ, CA, CT, HI, MA, MD, MN, MO, NC, NJ, NV, NY, OR, PA, RI, TN, TX, VA) have enacted laws requiring that imaging centers notify patients with heterogeneously or extremely dense breasts that they may be at greater risk of developing breast cancer.⁴⁰ Some states also require, even though there are no supporting data, that women with dense breasts discuss potential benefits from additional screening (e.g., ultrasound) beyond mammography with their physicians.⁴¹

Figure 1.

Mammograms of varying breast densities from a craniocaudal view: (a) almost entirely fat, (b) scattered fibroglandular densities, (c) heterogeneously dense, and (d) extremely dense.

ACRIN 6666, the largest trial comparing the addition of screening ultrasound to mammography in women with dense breasts and at least one other risk factor, demonstrated a detection rate of 4.3 additional cancers per 1000 women screened.⁴² This increased detection was accompanied by an increase in biopsy rates from 2% to 5% of all women screened after adding ultrasound, with only 7.4% of the additional biopsies being positive for cancer – indicating a high false positive rate.⁴² Moreover, the ultrasound exams in ACRIN 6666 were performed by subspecialty-trained breast imagers, raising uncertainty about what the results would be for screening ultrasound performed by general community radiologists and/or technologists.⁴¹

BRCA1 and BRCA2 mutations

Women with BRCA1 and BRCA2 gene mutations have a very high risk of developing breast and ovarian cancer during their lifetime. Two meta-analyses estimate cumulative risk of breast cancer by age 70 to be 55% to 65% for women with BRCA1 and 45% to 47% for women with BRCA2.^43,44 Some carriers elect to undergo prophylactic mastectomy because of this increased risk. For women who don't choose this surgical option, there is debate about the best breast cancer screening strategy.

Generally, women with either of these mutations are advised to consider starting both screening mammography and screening MRI before the age of 40. In 1997, the Cancer Genetics Studies Consortium Task Force recommended that female carriers of BRCA1 or BRCA2 initiate annual mammograms between the ages of 25 to 35, using a consistent facility with prior films available for comparison.⁴⁵ Since then, the National Comprehensive Cancer Network has recommended both mammography and MRI screening starting at age 25,⁴⁶ the American College of Radiology recommends starting at age 30,⁴⁷ and the American Cancer Society recommends that individual preferences and circumstances guide the initiation of screening.⁴⁸

Early evidence indicates, however, that mammography is less sensitive for women with BRCA1 or BRCA2 mutations than for women without these mutations.⁴⁹ In addition, tumors in women with these mutations grow rapidly, such that a detectable malignancy could form in between breast cancer screening examinations.⁵⁰

There is mixed evidence concerning whether radiation, including from mammography, increases the risk of breast cancer in women with BRCA1 and BRCA2 mutations, with some studies showing that mutation carriers may be more prone to radiation-induced breast cancer than women without mutations⁵¹ and other studies not showing an increased risk from radiation.^52,53 While it is important to weigh the benefits of mammography against the risks, there is insufficient evidence to suggest that female carriers of BRCA1 or BRCA2 should avoid mammography due to radiation exposure.

There have been several limitations on the studies describing outcomes of using MRI to screen women at high risk of breast cancer.^54-62 These include limited numbers of screening rounds; lack of clarity regarding prevalent (first round of screening) and incident cancer detection rates; and varied underlying populations, equipment, protocols, and reporting of results. However, studies have consistently demonstrated that breast MRI is more sensitive than mammography or ultrasound in detecting hereditary breast cancer, though MRI has reduced specificity.^{54-56,60,63,64} Some breast cancers are identified with mammography but missed with MRI. Annual MRI screening of women with the BRCA1 mutation, in conjunction with annual screening mammography, has been shown in simulation modeling to be cost effective.^65,66 One approach to applying current guidelines to BRCA1 gene mutation carriers is to alternate MRI and mammography screening in six month intervals beginning at age 30 years.⁶⁷

Women with lifetime risk of breast cancer of >20%

In addition to women with BRCA genes, annual MRI screening is recommended for women with a lifetime risk of breast cancer > 20%, which includes women with a strong family history of breast or ovarian cancer and women treated with radiation for Hodgkin lymphoma.⁴⁸ Unlike mammography, MRI does not use ionizing radiation, thus limiting a known risk factor for developing breast cancer.

Potential benefits and risks

Potential benefits

Mortality reduction

Screening mammography has been associated with reduced mortality from breast cancer in women 40 to 70 years of age, with absolute risk reduction increasing with age. Figure 3 shows the breast cancer mortality risk ratios found in RCTs of breast cancer screening. As shown in Table 1, adapted from a systematic review of the benefits and risks of screening mammography,⁶⁸ the number of breast cancer deaths averted with screening mammography in the next 15 years out of 10,000 women undergoing annual screening mammography for 10 years is 1-16 for women aged 40 years, 3-32 women aged 50 years, and 5-49 for women aged 60 years.

Figure 3. Breast Cancer Screening RCTs.

Results of a meta-analysis of randomized clinical trials of breast cancer screening. From Glasziou P, Houssami N. The evidence base for breast cancer screening. Prev Med. 2011 Sep;53(3):100-2; with permission.

Table 1.

Estimated benefits and risks of mammography screening for 10,000 women who undergo annual screening mammography over a 10-year period.

Age of women, years	No. of Breast Cancer Deaths Averted With Mammography Screening Over Next 15 Yearsa	No. of Women (95% CI) With ≥1 False-Positive Result During the 10 Yearsb	No. (95% CI) With ≥1 False Positive Resulting in a Biopsy During the 10 Yearsb	No. of Breast Cancers or DCIS Diagnosed During the 10 y That Would Never Become Clinically Important (Overdiagnosis)c
40	1-16	6130 (5940-6310)	700 (610-780)	?-104d
50	3-32	6130 (5800-6470)	940 (740-1150)	30-137
60	5-49	4970 (4780-5150)	980 (840-1130)	64-194

^aNumber of deaths averted are from Welch and Passow;⁹⁹ the lower bound represents breast cancer mortality reduction if the breast cancer mortality RR were 0.95 (based on minimal benefit from the Canadian trials^100,101), and the upper bound represents the breast cancer mortality reduction if the RR were 0.64 (based on the Swedish 2-County Trial¹⁰²).

^bFalse-positive and biopsy estimates and 95% CIs are 10-year cumulative risks reported in Hubbard et al⁶ and Braithwaite et al.¹⁰³

^cOverdiagnosed cases are calculated by Welch and Passow;⁹⁹ the lower bound represents overdiagnosis based on results from the Malmö trial,⁹⁵ whereas the upper bound represents the estimate from Bleyer and Welch.⁹⁶

^dThe lower bound estimate for overdiagnosis reported by Welch and Passow⁹⁹ came from the Malmö study.⁹⁵ The study did not enroll women younger than 50 years.

(Adapted from Pace LE, Keating NL. A systematic assessment of benefits and risks to guide breast cancer screening decisions. JAMA. 2014;311(13):1327-1335; with permission.)

Decreased morbidity from therapies for cancers detected at earlier stages

When screening detects cancer at an earlier stage, a woman can undergo less invasive therapies than she would if the cancer were diagnosed at a later stage. Compared to cancers detected with physical examination (palpable tumors), breast cancers detected with screening mammography are usually smaller, less likely to have metastasized, more likely to be treated with breast conservation surgery (56% versus 32%), and less likely to receive adjunct chemotherapy (28% versus 56%).^69,70 Thus, breast cancer screening is associated with increased treatment options and decreased morbidity from invasive therapies such as mastectomy and complete axillary node dissection.⁷¹

Psychological benefit

Another benefit of screening mammography is the peace of mind some women receive from participating in screening and receiving a negative or “normal” mammogram. This benefit has not been well-documented or studied and is often ignored in risk-benefit discussions regarding population-based breast cancer screening.

Potential Risks

Pain and discomfort

During a mammogram, a woman's breasts are compressed in order to create uniform breast density, improve image resolution by reducing motion artifact, and reduce radiation dose. A systematic review of studies evaluating physical pain and discomfort from mammography found that reports of pain were associated with women's menstrual cycles and expectations, rather than from mammographic compression.⁷² While most women experienced some discomfort, few of these women considered compression a deterrent from undergoing screening.

Radiation exposure

Ionizing radiation can increase one's risk of developing breast cancer, as seen in women who have received therapeutic radiation to the chest (e.g., for Hodgkin lymphoma).^73-75 The mean glandular dose from mammography in the U.S. is 1 to 2 mGy (100 to 200 mrad) per view, amounting to 2 to 4 mGy (200 to 400 mrad) per standard two-view examination.^73,76 There is no way to know if and how many breast cancers are actually being caused by screening mammography. Still, the potential risk has prompted efforts to limit exposure by reducing the amount of radiation required for mammography screening, developing imaging modalities that do not use radiation (e.g., ultrasound and MRI), and modifying screening strategies for subpopulations especially vulnerable to radiation.^77,78

False positives

A false positive result occurs when a screening mammogram is interpreted as abnormal in a woman who does not have cancer. In the United States, the false positive rate is estimated to be 10% of women screened with mammography.^79,80 Table 1 shows estimates that out of 10,000 women screened annually with mammography for 10 years, 4,970 to 6,130 women will receive at least one false positive result in 10 years. It is estimated that 700 to 980 women who receive false positives undergo unnecessary biopsies. In a retrospective study that quantified the cumulative risk of receiving false positive results by following women who were continually enrolled in a U.S. health plan for a decade, the authors estimated the cumulative risk of a woman receiving at least one false positive result as 49.1% (95% CI, 40.3-64.1) after 10 mammograms and 22.3% (95% CI, 19.2-27.5) after 10 clinical breast exams.⁸¹ The cumulative rates of breast biopsies for women without breast cancer were 18.6% (95% CI, 9.8-41.2) after 10 mammograms and 6.2% (95% CI, 3.7-11.2) after 10 clinical breast exams.

The risk of false positives varies depending on the characteristics of women screened, the screening modality used, and the radiologist interpreting the exam.⁸² Risk increases with patient variables (e.g., younger age, higher number of previous breast biopsies, family history of breast cancer, current estrogen use) and interpretive variables (e.g., longer time between screening, failure to compare current with previous mammograms), and the radiologist's tendency to interpret mammograms as abnormal has the greatest effect on false positive risk.

False positive rates may vary by country as well.⁸³ One review of 32 breast cancer screening programs noted global variation in the percentage of mammograms interpreted as abnormal (ranging from 1.2% to 15%) and the number of biopsies performed (ranging from 5% to 85.5%).⁸⁴ A higher percentage of mammograms interpreted as abnormal in North America was noted, despite cancer rates being similar.⁸⁴ False positive rates may be even higher with the use of additional screening modalities such as CAD and MRI. Studies suggest that 8% to 15% of women who undergo screening MRI are called back for additional evaluation and 3% to 15% will ultimately undergo breast biopsies.^55,56,85

Anxiety

Emotional discomfort and anxiety can result from being called back for diagnostic work-up after an abnormal mammogram. Several studies demonstrate that women who receive clear communication about negative screening results experience minimal anxiety about screening, while women who are recalled for additional diagnostic evaluation experience transient to persistent levels of anxiety.⁸⁶ In one study, women who initially received abnormal screening results but were subsequently found not to have cancer still experienced worry that affected their mood or functioning three months after screening.⁸⁷ A systematic review found that women who experience anxiety after a false positive mammography result receive more frequent future screening mammograms.⁸⁸

False negatives

All breast cancer screening modalities can yield a false negative: a negative screening result when the patient does have breast cancer, as proven by biopsy. For example, a lesion may not be viewable on imaging. Both women and their clinicians need to learn to not be falsely reassured by a normal imaging exam in the setting of a clinically detectable mass, as this can lead to delays in diagnosis and treatment.

Cost

In the U.S., mammography is estimated to account for almost $8 billion in annual health care expenditures.^89,90 Modeling estimates of screening mammography in the U.S. indicate that screening 85% of women would cost $10.1 billion with annual screening of women age 40 to 84 years (the American Cancer Society recommendation); $2.6 billion with biennial screening of women age 50 to 69 years (the European approach); and $3.5 billion with biennial screening for women age 50 to 74 years, personalized risk-based screening for women < age 50 years, and screening based on comorbid conditions for women ≥ age 75 years (USPSTF recommendations).⁸⁹ Other imaging modalities (e.g. MRI) are more expensive than mammography, and they can result in greater recall for diagnostic evaluation.

Overdiagnosis

Overdiagnosis occurs when a woman is diagnosed with a breast cancer that would not have manifested with symptoms during a woman's lifetime; in other words, she would die of other causes before developing symptoms of breast cancer.⁹¹ Once diagnosed, a woman might undergo treatments such as surgery, radiation, chemotherapy, and hormonal therapy, resulting in unnecessary costs and harms. While it is difficult to determine the magnitude of overdiagnosis, the estimated range of breast cancer cases being overdiagnosed is between 7% to 50%.^92-96 As shown in Table 1, one estimate is that among 10,000 women undergoing screening mammography annually for ten years, 30 to 194 women will be overdiagnosed with either DCIS or invasive breast cancer. Unfortunately, there is currently no way to determine at diagnosis of asymptomatic DCIS or invasive breast cancer whether or not the lesion will manifest symptomatically and ultimately cause harm to the woman; therefore, the current standard is to recommend treating all diagnosed DCIS and invasive breast cancer.

Interpretation of screening mammography results

Clinicians receive screening mammography results for their patients in standardized lexicon using the American College of Radiology's Breast Imaging Reporting and Data System (BI-RADS).⁹⁷ Screening mammograms interpreted as normal or benign (BI-RADS assessment categories 1 and 2, respectively) correspond with a clinical management recommendation of continued routine screening, though the decision to continue screening should be based on the woman's preferences. Almost all abnormal screening mammograms are interpreted as BI-RADS assessment category 0, which indicates an incomplete assessment and request for additional diagnostic mammographic views and/or ultrasound. Some radiologists will provide a “probably benign” assessment at screening and recommend short-term follow-up mammography in 6 months. This designation corresponds to a radiologist's belief that the finding harbors < 2% of malignancy. Rarely, radiologists will provide a BI-RADS 4 or 5 category assessment, deeming an imaging finding as suspicious for malignancy; these designations are usually reserved for after a complete diagnostic work-up has been completed.

Communication

Communication with women before screening

Before women begin routine screening, clinicians should address patients’ fears, concerns, and desires regarding screening, along with their underlying risk. Women may have an incorrect perception of their risk of dying of breast cancer. While 1 in 8 women will be diagnosed with invasive breast cancer during their lifetime, the majority of women diagnosed will not die from their breast cancer. In addition, the majority of breast cancers are diagnosed in older women.

In terms of discussing breast cancer screening with women in order to facilitate informed decision making, physicians have traditionally been more likely to discuss the benefits than the harms of screening and frequently do not ask about women's preferences.⁹⁸ Therefore, physicians should make an effort to discuss both the benefits and the harms of screening with their patients, as presented in Box 1. In addition, once a woman has decided to undergo screening mammography, her physician should provide her with information to help her prepare for the exam and facilitate clear, useful test result interpretation.

Box 1 Topics to discuss with patients when deciding whether to participate in screening.

Most Women Are at Lower Risk of Breast Cancer Diagnosis Than May Be Perceived

• Most women have a lower risk of breast cancer death than they might think. The “1 in 8” statistic refers to how many women will be diagnosed with breast cancer over their lifetime, with most women diagnosed in their 70s and 80s, not how many women will die of breast cancer over a certain period of time.

Mammography Is Not a Perfect Screening Test

• While mammography will detect most cancers, some cancers will be missed, and some women will die of breast cancer regardless of whether they are screened.

• Often, women are called back for further testing because of an abnormality that is not cancer; this is called a “false-positive” result.

• Most women diagnosed with breast cancer will be cured regardless of whether the cancer was found by a mammogram.

• Some cancers that are found would have never caused problems (i.e., symptoms). This is called “overdiagnosis.”

Making a Decision about Mammography

• Some expert groups, including the United States Preventive Services Task Force, recommend that women aged 50 to 74 years undergo a screening mammogram every 2 years. Other expert groups recommend screening mammograms beginning at age 40 every 1-2 years.

• Whether you are likely to benefit from starting mammograms earlier or having them more frequently depends on your risks for breast cancer and your values and preferences.

• Each woman may feel differently about the possibility of having a false-positive result or being diagnosed with and treated for cancer that might not have caused problems. It is important for you to consider what these experiences might mean for you. It is also important to consider how you might feel if you decide not to undergo screening mammography and you are later diagnosed with breast cancer, even if the likelihood that mammography would have made a difference is small.

(Adapted from Pace LE, Keating NL. A systematic assessment of benefits and risks to guide breast cancer screening decisions. JAMA. 2014;311(13):1327-1335; with permission.)

Communication with women after screening

If a woman receives an abnormal screening result, she might be anxious about the possibility of having breast cancer. Clinicians should help women navigate further testing and explain the likelihood that it could be a false positive based on the reported BI-RADS assessment. Women should understand that a positive screening result does not mean that they have cancer, only that they need additional examinations to rule out breast cancer. Similarly, women should understand that it is possible to receive a false negative result, as no screening test is perfect.

Conclusion

Mammography is the best-studied breast cancer screening modality and the only recommended imaging tool for screening the general population of women. Deciding when and how to participate in screening should involve a personalized discussion between a woman and her provider, weighing the individual breast cancer risk factors and competing co-morbidities. In addition, a balanced discussion regarding both the benefits and risks of routine screening is warranted.

Key points.

• Mammography is the best-studied breast cancer screening modality and the only recommended imaging tool for screening the general population of women.

• Overall, there is a modest mortality benefit from routine breast cancer screening with mammography at the population level.

• Potential harms of routine screening include false negative results, false positive results with undue anxiety and benign biopsies, and overdiagnosis.

• Efforts should be made to help women make more informed decisions about participating in breast cancer screening.