RISK FACTORS & RISK ASSESSMENT
Breast cancer is the most commonly detected non-skin cancer in women and the second leading cause of cancer death (see also Chapter 17-07). Breast cancer risk is increased with age and with a family history of breast cancer. Women who drink more than two alcoholic drinks per day are at increased risk for breast cancer, and exercise is associated with a decreased risk of breast cancer. Dietary intake has not been conclusively associated with breast cancer risk. Breast density is a risk factor for breast cancer; women with denser breasts as measured with mammography are at increased breast cancer risk. Although some states mandate that women with increased breast density on mammography be notified, it is not currently known what women can do to decrease this risk.
Various models have been used to predict a woman's risk for breast cancer. The National Cancer Institute has developed the Breast Cancer Risk Assessment Tool (http://www.cancer.gov/bcrisktool/), which is based on the Gail Model, a statistical model that uses the woman's own personal information to calculate a woman's risk of developing breast cancer in the next 5 years. Factors that are included are (1) the woman's age, (2) age at which she had her first menstrual period, (3) age at delivery of first live child, (4) number of first-degree relatives with breast cancer, (5) history of any breast biopsies, and (6) history of atypical hyperplasia. The outcome is a woman's 5-year risk of developing breast cancer compared with women of the same age and ethnicity. The model has been validated in white women and has been evaluated in black women and found to be relatively accurate, although it may underestimate the risk in black women with a history of previous breast biopsies. It has yet to be validated in women of other ethnicities. Women with a family history of breast, ovarian, tubal, or peritoneal cancer may need to be considered for genetic counseling, BRCA1 or BRCA2 testing, chemoprevention, or prophylactic surgery. The Gail model is less useful in women with an extensive family history of breast cancer (beyond first-degree relatives) and so other models have been proposed for use in these populations. These include the Ontario Family History Risk Assessment Tool, the Manchester Scoring System, the Referral Screening Tool, the Pedigree Assessment Tool, and the Family History Screen.
PRIMARY PREVENTION: CHEMOPREVENTION
In addition to lifestyle modifications, such as exercise and moderation of alcohol intake, chemoprevention of breast cancer is an option for some women. The selective estrogen receptor modifiers (SERMS) tamoxifen and raloxifene have both been shown to reduce invasive breast cancer rates in high-risk women. However, there are risks associated with SERM treatment. Tamoxifen is associated with an increased risk of endometrial cancer and deep venous thrombosis (DVT). Although raloxifene is not associated with an increased risk of endometrial cancer, the risk of DVT remains. Breast cancer risk increases with age, but the risk of adverse effects from chemoprevention does as well. Aromatase inhibitors, such as exemestane, show promise for breast cancer prevention but are not currently US Food and Drug Administration (FDA) approved for this indication. The United States Preventive Services Task Force (USPSTF) recommends that clinicians offer to prescribe risk-reducing medications, such as tamoxifen, raloxifene, or aromatase inhibitors, in women who are at increased risk for breast cancer and at low risk for adverse medication effects. Since the clinical trials of tamoxifen and raloxifene for breast cancer prevention used a 1.66% 5-year risk of breast cancer for decision making about initiation of therapy, this risk level is often used as a guide for medication treatment.
SECONDARY PREVENTION: BREAST CANCER SCREENING
Traditional breast cancer screening modalities include screening mammography, clinical breast examination, and breast self-examination. Breast cancer screening is discussed in detail in Chapters 1-08, 17-07, and 39-15 and in the references below.
et al. Breast cancer screening for women at average risk: 2015 guideline update from the American Cancer Society. JAMA. 2015 Oct 20;314(15):1599–614.
et al. Screening for breast cancer: U.S. Preventive Services Task Force recommendation. Ann Intern Med. 2016 Feb 16;164(4):279–96.
US Preventive Services Task Force; Owens
et al. Medication use to reduce risk of breast cancer: US Preventive Services Task Force recommendation statement. JAMA. 2019 Sep 3;322(9):857–67.
et al. Quantifying the benefits and harms of screening mammography. JAMA Intern Med. 2014 Mar;174(3):448–54.