Agency for Research on Cancer has concluded that shift work, particularly at night, is probably carcinogenic to humans.164 Factors that are not associated with breast cancer risk Abortion There are persistent claims that women who have had an abortion are at increased risk for developing breast cancer based on early studies that have since been deemed methodologically flawed by the American College of Obstetricians and Gynecology.165 Indeed, a large body of solid scientific evidence, including a review by a panel of experts convened by the National Cancer Institute in 2003, confirms that there is no link between breast cancer and abortion (either spontaneous or induced).166 Bras Although internet rumors have suggested that bras cause breast cancer by obstructing lymph flow, there is no scientific basis or evidence to support this claim. A recent population-based study of more than 1,500 women found no association between wearing a bra and breast cancer.167 Breast implants No association has been found between breast implants and risk of breast cancer; however, there is evidence that women with implants are at increased risk of a rare type of lymphoma.168 In addition, breast implants can obstruct the view of breast tissue during mammography. Women with breast implants should inform the mammography facility about the implants during scheduling so that additional x-ray pictures (called implant displacement views) may be used to allow for more complete breast imaging. Chemoprevention and prophylactic surgery Chemoprevention The use of drugs to reduce the risk of disease is called chemoprevention. Currently, the US Food and Drug Administration has approved two drugs to help lower the risk of breast cancer in high-risk women: tamoxifen and raloxifene (postmenopausal women only). These drugs are classified as selective estrogen receptor modulators (SERMs) because they block estrogen in some tissues of the body, but act like estrogen in others. A large meta-analysis, including more than 83,000 high-risk women, found that SERMs reduced breast cancer risk by 38% over 10 years.169 Although the benefit is limited to ER+ disease, these drugs lower the risk of both invasive cancer and DCIS. However, SERMs are associated with some side effects, including hot flashes, nausea, and fatigue. Premenopausal women taking tamoxifen can also experience menstrual changes. More serious side effects are rare but include blood clots and endometrial cancer.169 Clinical trials have shown that another class of drugs – aromatase inhibitors – also reduce breast cancer risk (by more than half) among high-risk postmenopausal women.170 As a result, the US Preventive Services Task Force recently expanded their recommendations to include aromatase inhibitors, as well as SERMS, for breast cancer risk reduction in high-risk women.171 Aromatase inhibitors can decrease bone density, so women taking these drugs must be monitored for osteoporosis. Prophylactic surgery Women at very high risk of breast cancer (such as those with pathogenic BRCA gene variants) may elect prophylactic (preventive) mastectomy. Removal of both breasts reduces the risk of breast cancer by 90% or more.172 Prophylactic salpingo-oophorectomy (surgical removal of the fallopian tubes and ovaries) reduces the risk of ovarian cancer, but the benefit for breast cancer in high-risk women is less clear and may be limited to 20 Breast Cancer Facts & Figures 2019-2020 BRCA2 mutation carriers.173 Importantly, however, many women who elect prophylactic surgery would not have developed cancer. Women considering these options should discuss the benefits and limitations with their doctor, and a second opinion is strongly recommended. See page 23 for further discussion of contralateral prophylactic mastectomy in women diagnosed with unilateral breast cancer. Breast Cancer Screening American Cancer Society recommendations for the early detection of breast cancer vary depending on a woman’s age and include mammography, as well as magnetic resonance imaging (MRI) for women at high risk. The recommendations for average-risk women were most recently updated in 2015 (see box, opposite page);174 recommendations for women at increased risk will be updated in 2020. Mammography Mammography is a low-dose x-ray image of breast tissue. Although early mammographic images were on x-ray film, digital technology, in which a 2-dimensional (2D) image of breast tissue is captured electronically and viewed on a monitor, has largely replaced screen-film mammography. Digital mammography has improved sensitivity for women under age 50 and those with dense breast tissue.175 Early detection of breast cancer by mammography reduces the risk of breast cancer death and increases treatment options, including less extensive surgery and/or the use of chemotherapy with fewer side effects, and sometimes, the option to forgo chemotherapy. Combined analysis of breast cancer screening in randomized trials has demonstrated an overall reduction in breast cancer deaths of about 20%.176 More recent results from organized mammography programs in Europe and Canada indicate that the risk of breast cancer death was reduced by more than 40% among women who were screened.177-179 Women should also be