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 and calculates the woman’s risk of developing breast cancer in the next 5 years by considering the following factors: (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 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. 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 discuss chemoprevention with women at high risk for breast cancer and at low risk for the adverse effects of chemoprevention. Clinicians should inform patients of the potential benefits and harms of chemoprevention. Breast cancer risk increases with age, but the risk of adverse effects from chemoprevention does as well. Since the clinical trials of tamoxifen and raloxifene for breast cancer prevention used a 1.66% 5-year risk 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 using tomosynthesis in combination with digital mammography. JAMA. 2014 Jun 25;311(24):2499–507.
et al.. Twenty-five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial. BMJ. 2014 Feb 11;348:g366.
et al.. Use of medications to reduce risk for primary breast cancer: a systematic review for the U.S. Preventive Services Task Force. Ann Intern Med. 2013 Apr 16;158(8):604–14.
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.
et al.. Quantifying the benefits and harms of screening mammography. JAMA Intern Med. 2014 Mar;174(3):448–54.