Breast cancer remains the most common cancer in American women, excluding cancers of the skin, and accounts for 29% of all female cancer in the United States. The lifetime risk of an American women being diagnosed with breast cancer is 1 in 8. The American Cancer Society (ACS) estimates that in 2016 there will be 232,340 cases of invasive breast carcinoma and an additional 64,640 cases of in situ disease.¹ In addition, 39,620 deaths are estimated to occur in 2016. Everyone knows someone who has been affected by breast cancer, and breast cancer advocacy remains strong in the public eye. Consequently, breast cancer screening has become highly politicized in the United States. Heated debates regarding the efficacy of mammographic screening for breast cancer have become a frequent lay media occurrence.

With a documented 34% decrease in breast cancer mortality since 1990, lung cancer has surpassed breast cancer in terms of mortality. The relative contribution of mammographic screening versus the improvement in adjuvant treatment remains controversial. Breast cancer screening has evolved from early screening trials in the 1960s to the early 1980s with film screen mammography; some studies used single view and interval screening every 2 to 3 years. Current standard mammographic screening includes two-view mammographic imaging with more than 93% performed with digital technology on dedicated mammography units, with specialty trained radiologists and technologist, and medical physicist closely overseeing the quality assurance and quality control of the operational mammographic units.

In 1992 congress enacted a law that went into effect in 1994 and ensured that women had access to quality screening mammograms. The U.S. Food and Drug Administration (FDA) developed and administered the Mammography Quality Standard Act (MQSA) regulations. As of November 1, 2016 there were 8698 certified facilities and 13,053 accredited units that meet a minimum baseline quality standard and are certified to legally operate in the United States and the total annual mammographic procedures reported up to November 1, 2016 were 38,541,887.²

Knowledge of the limitations of mammographic screening continues to drive development and investigations of new technologies. Some recent developments such as digital breast tomosynthesis (DBT) are quickly becoming mainstream. Preliminary data suggests that DBT will address some of the limitations of traditional mammography such as imaging the women with dense breast tissue and decreasing recall rates which are mostly due to overlap of tissue on mammography. As new technologies become available, physicians will continue to collect data and make screening recommendations hopefully not based on public opinion but on data.

In 1968, the World Health Organization published the landmark manuscript on screening for disease.³ The basic principles for screening a population are summarized in Table 67-1. Breast cancer meets most of the requirements for screening since the disease is common and important, there is an asymptomatic period during which the detection of the disease can be of benefit because of effective treatment, and the test used for screening, that is mammography, is inexpensive and readily available. Screening mammography has moderate sensitivity; however, it lacks specificity. As of 2016, no other imaging modality or clinical assessment has been shown by randomized clinical trials to decrease breast cancer mortality like mammographic screening has.

In the past it was thought that, although the mortality benefit was not well documented in literature, there was no harm in encouraging women to utilize breast self-exam (BSE) as a screening tool.^4,5 There have been two large randomized control studies that were designed to evaluate the effectiveness of BSE. The Russian WHO study randomized women aged 40 to 64 to either a BSE educational program or a control group.⁶ At the end of 16 years a higher number of benign and malignant tumors were detected in the self-examination group, but the overall mortality was not different between the two groups. In Shanghai 267,040 women aged 31 to 64 were randomly assigned to extensive BSE training utilizing silicone breast models and two additional reinforcement sessions or to a control group. At that time mammography was not readily available to the population and it was seen as an ideal population to study. The women were followed over 10 to 11 years and although the BSE group detected more benign breast lesions every year and the lesions were smaller in size, there was no difference in the stage of the cancer diagnosed or the overall mortality between the two groups.^7,8 Additional cohort and case control studies have demonstrated that there is no significant difference in mortality or frequency of terminal breast cancer between women who practiced BSE and matched controls.^9,10

The U.S. Preventative Service Task Force (USPSTF), the Canadian Task Force on Preventive Health Care, and the ACS have determined that based on the lack of decreased mortality or early detection benefit, and in the setting of proven harm, women should not be routinely taught self-breast exam as there is no clear benefit and there is a documented potential harm from unnecessary biopsies driving higher cost.^7,11,12

In recent years the efficacy of the clinical breast exam (CBE) has been called into question, although it is routinely used as an adjunct to mammography, and in some countries, as the main approach to breast cancer screening. Up until recently there was no randomized control study that evaluated the mortality benefit of CBE compared to controls and it was promoted based on indirect evidence from studies comparing CBE to mammographic screening^5,13–15. Canadian National Screening Study 2 (CNBSS-2) compared and followed 39,405 women aged 50 to 59 who were randomized either to a control arm of annual CBE, or annual mammography and CBE.¹⁶ The women were followed for 13 years and demonstrated there was no significant difference in the breast cancer mortality between the two study arms. Based on this and other studies, it has been inferred that a well-conducted CBE can be just as effective as mammographic screening for breast cancer detection, although it was not clear if this could be translated to the clinical world. In studies looking at the CBEs in the clinical realm, the sensitivity has ranged from 69% to 31% depending on the age of the woman, the thoroughness/length of the exam, and the extent of additional breast cancer screening.^5,13 Studies have shown that in the community setting, CBEs are often significantly shorter and unstandardized bringing into question the external validity of studies documenting the sensitivity of CBEs.¹⁷ Support for CBE includes the fact that mammography would miss cancer without CBE. A small percentage of breast cancer, ranging from 4.6% to 5.7% throughout multiple studies, is detected on physical exam alone and missed on mammography.^18–21 However, addition of CBE to mammography has also been documented to increase the rate of false-positive results compared to mammography alone.²⁰

Currently, the recommendations on the utilization of CBE for breast cancer screening vary significantly between organizations. In 2009 the USPSTF stated that there is insufficient evidence to assess the benefits and harms of CBE beyond screening mammography in women greater than 40 years old. The ACS current guidelines state that for women in their twenties and thirties, CBE should be a part of periodic health exam and be used on an annual basis for screening in women age 40 and above.^7,17,22,23

Mammographic screening guidelines have remained a high-profile subject in the media, even more so after the 2009 controversial USPSTF mammographic screening guidelines were released. In 2002 the USPSTF performed a meta-analysis for the eight large prospective mammography trials designed to assess the effectiveness of mammography in reducing breast cancer mortality but only included data from seven trials. In their estimation, all the trials had limitations. USPSTF concluded that mammography reduced breast cancer mortality among women 40 to 74 years of age with a greater benefit in women age greater than 50. In 2002 the USPSTF recommended mammography screening every 1 to 2 years for women 40 years and older.²⁴ In 2009, this group updated their analysis to include data from the Age trial from the United Kingdom that randomized women ages 39 to 41 to annual screening mammography until age 48.²⁵ Once again, the Task Force found a 15% reduction in breast cancer mortality in favor of screening with an even greater benefit for women over 50. In addition, they reported that for women ages 40 to 49 the false-positive rate was the highest, with what they consider an unacceptable rate of additional imaging and unnecessary biopsies.¹¹ For these reasons, USPSTF changed their recommendations to consider starting mammographic screening at age 50. Media coverage was generally critical of the recommendations, noting concerns that delayed screening would increase breast cancer mortality and fear about government rationing of health care. Likely in part because of the controversy surrounding the 2009 recommendations, private and public insurers have generally continued to cover annual mammograms for women ages 40 to 50 years.²⁶ The Affordable Care Act requires private insurers and Medicare to cover annual mammography without cost sharing for women starting at 40 years.²⁷

There have been many analyses examining the same data with different conclusions depending on the critiques of each of the studies. Some investigators have dismissed many of the randomized prospective studies due to study flaws. In a 2011 Cochrane review, the investigators rated the quality of the eight eligible trials; only three were found to have adequate randomization. Interestingly, the trials with adequate randomization did not find any effect of screening mammograms on breast cancer deaths after 10 years (relative risk (RR) 1.02, 95% confidence interval (CI) 0.95 to 1.10).²⁸ However, other pooled estimates from all the trials and all age groups have shown that mammographic screening does provide a 20% breast cancer mortality reduction which is highly statistically significant.^29,30

The guidelines for breast cancer screening from some of the major organizations are summarized in Table 67-2. An important point to keep in mind is that the recommendations are aimed at average-risk women. Women that are high risk, as discussed in detail below, are not the target of these recommendations. In 2015 the ACS modified their guidelines for screening mammography with (a) strong recommendations where the benefit was clear and (b) qualified recommendation where there was clear evidence of benefit of screening but less certainty about the risk benefit ratio. Discussions between patients are provider is warranted for a final screening recommendation. The ACS recommends that women should have the opportunity to begin annual screening between the ages of 40 and 44 years (qualified recommendation). Women with average risk of breast cancer should undergo regular screening mammography starting at age 45 years (strong recommendation). Women aged 45 to 54 years should be screened annually (qualified recommendation). Women 55 years and older should transition to biennial screening or have the opportunity to continue screening annually (qualified recommendation). Women should continue screening mammography as long as their overall health is good and they have a life expectancy of 10 years or longer (qualified recommendation). The ACS does not recommend clinical breast examination for breast cancer screening among average-risk women at any age (qualified recommendation).³¹ In general, American College of Radiology (ACR) and the Society of Breast Imaging (SBI) follow the same recommendations: annual mammographic screening beginning at age 40 and continuing until life expectancy is less than 5 years. The USPSTF guidelines are different, in that recommendation is made against screening women 40 to 49 years of age and screening is recommended in a biennial period rather than on an annual period for women aged 50 to 74.

A variety of imaging modalities have been used to screen for breast cancer. They include both screen film and digital mammography, DBT, dynamic contrast-enhanced breast magnetic resonance imaging (DCE-MRI), and whole-breast ultrasound (WBU), either handheld or the recently FDA-approved automated WBU (AWBU). The technique, imaging protocol, utility, and associated controversial role for each of these modalities will be discussed here. However, it is worth reiterating that only mammography has been studied in large population randomized clinical trials, and only mammography meets the specific criteria for screening for disease (i.e., widely available, inexpensive, low risk, high sensitivity and specificity).

Mammography

Mammography continues to be the gold standard in screening for breast cancer. A mammogram is an x-ray of the breast used to depict differences in density. Mammograms can be obtained using film screen (also known as analog) or full-field digital technique. The first film-screen mammogram was acquired in 1969, the first year that x-ray units dedicated to breast imaging became available. In screen film mammography, x-ray beams are captured on a film cassette which is subsequently processed and a hard copy film image is produced.³¹ The transition to digital mammography began in the early 2000s.³² With digital mammography, x-ray beams are instead captured on a digital detector which converts these x-rays into electronic signals and a computerized image is produced.³³

Using either technique, the standard bilateral screening mammogram consists of four views: bilateral craniocaudal and bilateral mediolateral oblique views. “Craniocaudal” and “mediolateral oblique” indicate the direction of the x-ray beam. Photographs of a patient undergoing mammographic screening are seen in Fig. 67-1. Examples demonstrating the differences between screen film and digital screening mammograms are shown in Fig. 67-2.