Knowing about risk factors helps identify women with higher than average risk for developing breast cancer and determine who may benefit from increased observation and referrals to specialists. Similarly, women with average risk can improve their chances against developing the disease by learning which lifestyle factors are associated with increased risk and by modifying their behaviors. In either case, it is important that a woman's risk of breast cancer is routinely assessed and that risk reduction strategies are recommended.
A risk factor is any characteristic or behavior that increases the chances of developing a disease. Different measures of risk may be used for describing a woman's chances for developing breast cancer. The most commonly used measures are absolute and relative risk.
Age-Specific Probability of Developing Breast Cancer
in next 10 years is:
Or 1 in:
Source: American Cancer Society. Breast cancer
facts & figures 2011-2012.
Absolute risk describes the percentage chance that a person will develop a disease during a given period of time. It is a useful measure for helping to determine what proportion of the population is at risk for a specific disease. In the case of breast cancer, it is estimated that 12.4% of women born today will be diagnosed with breast cancer at some time during their lives, or roughly 1 in 8.1 However, the absolute risk for any given decade of life is lower.
The accompanying table shows the changes in absolute risk for different age groups when estimating risk over a 10 year period.2 Because rates of breast cancer increase with age, age-specific estimates are generally more meaningful than an estimate of lifetime risk.
Relative risk describes the chance of developing a disease for persons having a certain characteristic (or a behavior) compared with those not having that same characteristic. Relative risk may be expressed as a percentage (e.g., 50% increase in risk). More often, it is expressed as a ratio, preceded by the abbreviation RR (e.g., RR 1.5).
RR 1.0 = no increase or decrease in risk
RR 1.5 = 50% increase in risk
RR 2.0 = 100% increase in risk
RR 0.5 = 50% decrease in risk
Risk can be a source of confusion for patients. In a study where women were asked to estimate their risk of breast cancer, researchers found that 89% overestimated their lifetime risk by more than three times the actual risk.3 Overestimating risk can cause undue stress and anxiety, both of which can lead to an avoidance of screening and risk-reducing strategies. Of course, underestimating risk can be just as much of a concern. People are less likely to be proactive about their health if they aren't aware of the potential risks.
When discussing risk with patients, healthcare providers are encouraged to use the opportunity to correct any possible misunderstanding. Examples that compare absolute with relative risk may be helpful when reviewing with patients the types of risk factors associated with the development of breast cancer. It is vital to take into consideration the patient’s cultural beliefs, literacy levels, understanding of the disease, and emotional state.4 Providers should discuss all risk factors (e.g. gender, age, genetic factors, family history, personal history, previous proliferative lesions, obesity, physical inactivity, alcohol consumption, childbirth, breast feeding, breast density and hormone use) and possible risk reduction strategies with every woman. Reviewing these factors helps to identify those women that would benefit from a full risk assessment by a physician with experience in breast cancer risk model selection and interpretation, or by a cancer risk assessment program.5
There are many established risk factors for breast cancer. Different factors are associated with varying increases in risk. Some factors cannot be changed, such as gender, age, and hereditary factors. However, other factors, including those related to lifestyle, are potentially modifiable and can significantly impact a woman's individual risk for developing the disease. In addition to the types of risk factors associated with breast cancer, health providers should discuss with patients the specific evidence-based strategies for reducing individual risk. (See Risk Reduction Strategies below.)
Gender and Age
Female gender is the most important risk factor for breast cancer. The risk for females is 100 times that of males. The second most important risk factor is age. The older a woman, the greater her chances of developing the disease. As many as 95% of new cases occur in women 40 years of age and older.2
Breast cancer risk is increased for women having a first-degree biological relative (mother, sister, daughter) or a second-degree biological relative (grandmother, aunt, niece) with the disease. Having one first-degree relative with breast cancer approximately doubles a woman's risk; having two first-degree relatives with breast cancer increases risk about 3-fold. In general, the more biological relatives with breast cancer, especially relatives who were diagnosed before age 50, the higher a woman's breast cancer risk.6
Some cases of breast cancer are hereditary, resulting from a genetic defect inherited from a parent.
The most common genes related to hereditary breast cancer are BRCA1 and BRCA2. According to the National Cancer Institute, 55-65% of women with the BRCA1 mutation will develop breast cancer and 39% will develop ovarian cancer before the age of 70. Of women with the BRCA 2 mutation, 45% will develop breast cancer and 11-17% will develop ovarian cancer before the age of 70.7 BRCA mutations are more common among those of European ancestry, particularly among people with Ashkenazi Jewish ancestry, but also including women of Icelandic and French Canadian descent.8 Overall, it has been estimated that inherited BRCA1 and BRCA2 mutations account for 5% to 10% of breast cancer cases among white women in the United States.7
Breast cancer is a common feature of syndromes and diseases resulting from other genetic mutations as well, as detailed in the Table (below). 91011
Genes Related to Breast Cancer
Associated Syndrome or Disease
Early onset breast and ovarian cancer
Fallopian tube, pancreas, possibly cervix and uterus
Early onset breast and ovarian cancer
Early onset breast and ovarian cancer
TP53 and CHEK 2
Soft tissue and bone sarcomas, leukemia, brain, adrenocortical malignancies
Personal History of Breast Cancer: A woman who has had breast cancer in one breasthas a 3 to 4-fold increase in risk of developing a new cancer in the opposite breast or in another part of the same breast. The amount of risk depends on the presence of other factors, such as a BRCA mutation. Carcinoma in situ (LCIS and DCIS) also increases a woman's risk for developing invasive breast cancer. The level of risk is modified by other factors, such as menopausal status, family history, time since biopsy, and treatment.7
Personal History of Other Cancers:The association of other cancers with increased risk is usually due to genetic factors (See Genetic Factors above). The risk of developing breast cancer is greater in women who have been diagnosed with cancer of the endometrium, ovary, colon, or other organs.10
Previous Diagnosed Proliferative Lesions:Women with different types of benign breast lesions have varying levels of risk for developing subsequent breast cancer. Research suggests that nonproliferative changes may have little to no effect on breast cancer risk. Proliferative changes without atypia are associated with a small increase in relative risk, from 1.5 to 2.0. Proliferative changes with atypia, including atypical lobular hyperlasia (ALH) and atypical ductal hyperplasia (ADH) increase relative risk by 4 to 5-fold.1112 Risk is higher still (10-fold) when the atypia is multifocal.10
Radiation to the Chest:Therapeutic radiation to the cheststrongly increases the risk of breast cancer for women who were treated with therapeutic radiation as children or young adults (e.g., treatment for Hodgkin disease or non-Hodgkin lymphoma). Risk is highest if radiation was received during adolescence; if after age 40, radiation therapy to the chest does not seem to increase breast cancer risk.6
The risk appears to be similar for women who are survivors of atomic bomb or nuclear plant accidents.10 Repeated chest CT scans and diagnostic chest x-rays may also contribute to a small increase in the risk of developing breast cancer, particularly for women with an inherited BRCA mutation.1013
Diethylstilbestrol (DES): Women who took DES, a synthetic form of estrogen hormone previously prescribed to prevent miscarriage (from 1940 to 1971), may have a slightly increased risk of breast and ovarian cancer. Similarly, the daughters of these women may also have a slightly higher risk of breast and ovarian cancer.6
Breast Density: Breast density is determined by the ratio of fat to fibroglandular tissue in the breast as imaged on a mammogram. Radiologists classify density into four categories: (1) almost entirely fatty (10% of women); (2) scattered areas of fibroglandular density (40% of women); (3) heterogeneously dense (40% of women); and (4) extremely dense (10% of women). Women in the latter two categories are considered to have dense breasts. The assessment of density is currently qualitative and visual only, rendering density classification subjective and imprecise. Given the current system of classification, 50% of women who undergo screening mammography in California will be subject to California Senate Bill 1538 and, therefore, will receive written notice that they have dense breasts.14
Research suggests that the most important determinant of breast density is inheritance, although endogenous hormone levels are also known to affect density.1015 Whether current or past breast density serves as the more accurate risk predictor remains an area of controversy, as do methods of measurement.16
Women with dense breasts are at greater risk of breast cancer. Some studies have reported a 4-6 fold increase in relative risk for women with mammographically dense breasts.17 However, according to the California Breast Density Information Group, this estimate may be misleading because most studies compare the risk of the 10% of women in the highest “extremely dense” category with the 10% of women in the lowest “almost entirely fatty” category. This comparison is not relevant for the other 80% of women. When risk is analyzed compared to average breast density (between scattered areas of fibrograndular density and heterogeneously dense), the risk of breast cancer for the women with heterogeneously dense breasts appears to be 1.2 times greater, while the risk for women with extremely dense breasts is approximately two times greater.14
Dense breast tissue also contributes to risk because it decreases the sensitivity of mammography. This is referred to as “masking” and occurs when tissue obscures a cancer. Mammographic sensitivity may be reduced by as much as 10-20% for patients with dense breasts. Women with dense breasts should continue to receive screening mammographies; mammography is the only screening tool shown to lower breast cancer mortality for all categories of density.14
For most women with dense breasts, risk increases only slightly. There are other important risk factors to consider. Besides age and sex, the strongest risk factors for breast cancer are:
family history of a first-degree relative with premenopausal breast cancer, a male relative with breast cancer, or a first- or second-degree relative with ovarian cancer
personal history or familial history of BRCA mutation
personal history of atypia, such as atypical ductal hyperplasia (ADH), atypical lobular hyperplasia (ALH) or lobular carcinoma in situ (LCIS) on a previous breast biopsy
Reviewing these risk factors helps to identify those women who would benefit from a full risk assessment by a physician with experience in breast cancer risk model selection and interpretation, or by a cancer risk assessment program.5
Information for Every Woman Counts (EWC) Providers
The state of California has become the fifth state with a breast density notification law (effective April 1, 2013). Senate Bill 1538 requires that women with dense breast tissue be notified after undergoing screening mammography. (See the California Legislative Information website for the full text.) 5
Factors that Increase Estrogen Exposure:
early onset of menstruation (before 12)
late menopause (after 55)
not having children, or giving birth to a first child after 30
recent use of menopausal hormones with estrogen
and progestin (combined HRT)
use of oral contraceptives within the
past 10 years
Estrogen is essential to the development of the female reproductive system. It also functions to help lower cholesterol, regulate mood, and fortify bones. However, estrogen also contributes to breast cancer risk. In general, the higher a woman's lifetime exposure to estrogen, the greater her risk.
The connection has to do with the fact that both healthy and abnormal cells can contain estrogen receptors, a type of molecule that stimulates cell growth when it comes in contact with estrogen. Lacking exposure to estrogen, certain cancerous cells would stop growing and eventually die.18
Estrogen exposure is increased with the early onset of menstruation (before 12) and late menopause (after 55). Similarly, women who have had no children (nulliparity), or their first child after age 30, have a slightly higher risk due to increased estrogen exposure. Not breastfeeding also increases a woman's risk since breastfeeding, like pregnancy, suppresses estrogen levels. Recent use of menopausal hormones with estrogen and progestin (also called combined hormone replacement therapy, or combined HRT) is associated with an increased risk of developing breast cancer, with higher risk associated with longer use. Risk appears to diminish within 5 years of discontinuation. The use of estrogen alone (without progestin) after menopause does not appear to increase breast cancer risk; however, some studies have suggested increased risk of both breast and ovarian cancer with use lasting longer than 10 years.6 Studies have also found that both combination and estrogen-alone hormone use renders mammography less effective for detecting cancer early.6 Findings from studies of oral contraceptives have suggested that risk is slightly increased for women who currently use this form of birth control but not for women who have discontinued use for more than 10 years.19
Obesity: Obesity is an established and modifiable risk factor for breast cancer. For postmenopausal women, estimates of excess risk are as high as 40%.20 The association between obesity and risk may be explained by higher circulating levels of estrogen caused from an excess of fatty tissue, the primary source of estrogen in postmenopausal women.
For women before menopause, obesity does not appear to increase breast cancer risk. In fact, some research suggests that a higher Body Mass Index in premenopausal women may actually be associated with lower risk. The reasons for this are unclear. Some attribute this inverse relationship to a decrease of estrogen associated with anovulation - an obesity-related condition that can sometimes cause irregular or longer menstrual cycles. However, a conclusive explanation remains elusive, with different studies having produced conflicting data.10
Alcohol: Alcohol consumption increases a woman's risk of breast cancer. The association is thought to be linked to estrogen. Alcohol alters how the body metabolizes this hormone, allowing for higher than normal levels circulating in the bloodstream.21 Most studies suggest that the risk of breast cancer increases as the amount of alcohol consumed increases. One alcoholic drink a day confers only a slight increase in risk while two to five drinks daily increases risk by about 1.5 times compared with women who do not drink alcohol.6
Other Known Risk Factors
Race/Ethnicity: In the U.S., breast cancer risk is slightly greater for white women ages 45 and older than for African American women in the same age group. For women under 45 years of age, the relationship is reversed; that is, breast cancer is more common in African American women than in whites. Asian, Hispanic, and Native-American women have a lower risk of developing breast cancer.6
Socioeconomic Status: In general, women from lower socioeconomic groups, regardless of their race/ethnicity, have a lower risk of developing breast cancer but higher mortality rates.1022
Geographic Residence: Geographic residence is associated with varying levels of breast cancer risk. Among women living in the U.S., breast cancer incidence rates range from 106.3 per 100,000 in New Mexico to 142.9 per 100,000 in Washington, D.C.23 Some variation may be explained by differences in population distribution of known risk factors, such as menstrual and reproductive factors. Research investigating other possible influences, such as environmental hazards, subgroups of susceptible individuals, and differences in medical practice/healthcare management, is ongoing.24
Height: Most of the research on height and breast cancer risk suggests an association. In a pooled analysis of seven prospective cohort studies, women who were 69 inches or taller were 20% more likely to develop breast cancer than women less than 63 inches tall.10
Factors With Uncertain Effect on Breast Cancer Risk
Research continues to explore other factors that may influence a woman’s risk of breast cancer. Results from numerous studies on the association of dietary fat and breast cancer risk have been inconclusive. Some have shown a mild to moderate association while others have found no clear link. Similarly, research on the relationship between cigarette smoking and breast cancer risk has produced mixed results. Some studies have found increased risk (both for smokers and for passive smoke exposure), while others have failed to establish an association. 6
Environmental chemicals may also play a role in risk. Although studies on humans have been inconclusive, the list of chemicals known to cause breast tumors in laboratory animals includes chemical solvents; chemicals used with the manufacturing of dyes; chemicals used in the manufacturing of rubber, vinyl, polyurethane foams or neoprene; fumigants and pesticides; gasoline additives; and pharmaceuticals, among others.25
Some studies support an association between working night shifts and an increased risk of developing breast cancer. Exposure to visible light at night is considered by some researchers to be explanatory since it suppresses the body's normal nocturnal production of melatonin which, in turn, may restrain tumor growth. 10
Factors with No Effect on Breast Cancer Risk
Factors with No Effect on Breast Cancer Risk:
Research has effectively debunked many popular myths about causes of breast cancer. Factors now known to have no influence on breast cancer risk include abortion, tubal ligation, caffeine, breast implants, electric blankets, hair dyes, antiperspirants, and bras. 610
Assessing a woman's individual risk for breast cancer engages the primary care provider and the patient in a discussion about breast cancer prevention, educates a woman about risk factors, and helps guide a personalized plan for risk reduction and early detection. A risk assessment should be made at each routine screening visit since a patient's personal risk factors will change over time. The strongest risk factors for breast cancer are:
family history of a first-degree relative with premenopausal breast cancer, a male relative with breast cancer, or a second-degree relative with ovarian cancer
personal or family history of BRCA mutations
previously diagnosed proliferative lesions or lobular carcinoma in situ
Providers should discuss risk reduction strategies and all risk factors with every woman, including gender, age, genetic factors, family history, personal history, previous proliferative lesions, obesity, physical inactivity, alcohol consumption, childbirth, breast feeding, breast density, and hormone use. Reviewing these factors helps to identify those women who should be referred for a full risk assessment by a physician with experience in breast cancer risk model selection and interpretation, or by a cancer risk assessment program.5
A complete breast cancer risk assessment includes an evaluation for known risk factors using a reliable risk assessment tool and obtaining a thorough personal and family history. The Breast Cancer History and Risk Assessment: Patient Information Form can be used with the Risk Assessment Table to help identify women who may be at increased risk of developing breast cancer.
Four of the most widely used mathematical models for estimating breast cancer risk are the Gail, Claus, BRCAPRO, and Tyrer-Cuzik. Each of these models can help determine what risk group a woman belongs to, but their value in determining individual risk is limited. This is in part because not all risks have been identified and in part because risk stratification is most accurate when risk factors are very strong. Most risk factors for breast cancer are relatively weak. In addition, much of the data used to design these models were drawn from women with existing breast cancer. It is unclear, therefore, how applicable they are to women who have no symptoms and are cancer-free.26
The Gail Model incorporates a number of established risk factors to estimate what lifetime and five year risk group a woman falls into for invasive breast cancer. A 5-year risk of 1.7% or higher is considered elevated. Although the model provides an accurate estimate of a woman’s risk of breast cancer, it cannot accurately predict which women will develop breast cancer and which will not. Women should be informed that the results are only approximate.27 In addition, this model is not recommended for use with patients having a strong family history since it excludes some well-established factors associated with hereditary breast cancer. When the model places a woman in a higher risk group, referral for a detailed risk analysis may be considered.26
The Gail model is the basis for the Breast Cancer Risk Assessment Tool, available online from the National Cancer Institute (NCI). Originally based on data from white women, it has since been updated for African American women and for Asian and Pacific Islander women living in the U.S. Risk estimates for Hispanic women are "subject to greater uncertainty than those for white women" since part of the model is derived from findings of studies with white women. Moreover, NCI notes that estimates for American Indian and Alaskan Native women "may not be accurate." Findings from additional studies with minority populations will be used for increasing the accuracy of the tool with these populations of women. The model is periodically updated to integrate the results of new studies.27
The Claus Model provides a more accurate estimate of risk for women with a family history of breast cancer by taking into account both maternal and paternal family history, second-degree relatives, and their ages at diagnosis. It also factors in a family history of ovarian cancer. However, unlike the Gail Model, the Claus Model does not include risk factors other than family history.28
The BRCAPRO incorporates six predictive models for inherited breast cancer and can be used to estimate the probability of having a BRCA1 or BRCA2 mutation in women whose family histories are suggestive of inherited breast and/or ovarian cancer. It can also be used to construct a family history tree to estimate a woman's chance of developing breast (or ovarian) cancer. Like the Claus Model, BRCAPRO does not incorporate risk factors that are unrelated to family history.26
The Tyrer-Cuzik Model predicts the development of breast cancer over 10 years. It includes family history of breast and ovarian cancer and factors such as age of menarche and history of atypical hyperplasia. Although this model has been found to have better predictive accuracy than other family-history models, one study concluded that it should not be used with women who have atypical hyperplasia.26
According to The National Cancer Institute, women with an inherited harmful mutation
in BRCA1 or BRCA2 are about five times more likely to develop breast cancer
than women without such a gene mutation.
Inherited breast cancer accounts for an estimated 5% to 10% of all breast cancers.29 Most inherited cases will be linked to BRCA1 and BRCA2 gene mutations. As discussed above, other genetic defects that may result in particular syndromes and diseases may also be related to breast cancer risk (See Genetic Factors above). However, even among women with genetic mutations, not all will develop breast cancer.
The U.S. Preventive Services Task Force (USPSTF) cautions against routine testing for genetic risk of breast cancer, noting that there are serious potential harms associated with genetic testing, and that for women with no family history of breast cancer, the risks of genetic testing outweigh any potential benefit. Test results can be ambiguous, and may give false-positive findings, creating undue stress, and potentially leading women to undergo unnecessary medical interventions. Negative results may lead patients to experience “survivor’s guilt” if other family members are known to have the mutation.30
For women with at least one family member with breast, ovarian, tubal, or peritoneal cancers that are associated with BRCA mutations, the USPSTF recommends that care providers administer a familial risk stratification tool to determine whether the woman would benefit from in-depth genetic counseling. Tools include:
Ontario Family History Assessment Tool
Manchester Scoring System
Referral Screening Tool
Pedigree Assessment Tool
These tools elicit information about family history factors that are correlated with increased likelihood of BCRA mutations, such as: diagnosis before age 50, bilateral breast cancer, presence of both breast and ovarian cancer, presence of breast cancer in a male family member, multiple cases of breast cancer in the family, one or more family members with two primary types of BCRA-related cancer, and Ashkenazi Jewish ethnicity.
The quickest and simplest of these tools are the FHS-7 and the Referral Screening Tool. The Referral Screening Tool can be found online at: www.breastcancergenescreen.org.
The Task Force notes that each tool has limitations and could not find sufficient evidence to recommend one tool over another. The USPSTF also found insufficient evidence to support a specific risk threshold for referral for testing.31
For women for whom genetic counseling is recommended, genetic counseling provides education about the probability of developing cancer, allowing them to make better informed decisions about undergoing genetic testing and/or preventative treatments. Genetic testing may reduce uncertainty about risk and provide reassurance if the test is negative. 32
Genetic testing can also provide the patient’s family members, including siblings and children, with valuable information about their level of risk. No clear consensus currently exists, however, about how to proceed when the patient refuses to disclose positive results of genetic testing to relatives. The courts agree that physicians are generally obligated to warn family members of their risk; however, consultation with geneticists, genetic counselors, or bioethicists is necessary should a patient refuse to consent to share the results of testing.33
According to The National Cancer Institute, 55-65% of women with an inherited harmful mutation in BRCA1 and 45% of women with a mutation in BRCA2 will develop breast cancer.17 In addition, these women have an increased risk of ovarian cancer and of developing these cancers at a young age (before menopause). It is therefore essential that women with these gene mutations be identified and referred for thorough evaluation. If gene testing is indicated, the genetic counselor will advise the woman of the benefits, limitations, and risks of testing - including those that have potential impact on a woman's emotions, social relationships, finances, and employment. If gene testing is not indicated, or if the patient chooses not to be tested, she should nevertheless be provided with a thorough cancer risk management plan.
It is estimated that as much as 27% of breast cancers are linked to modifiable risk factors.34 Clearly, the effective promotion of healthy behaviors can have a significant effect on incidence. Risk reduction strategies should be discussed with patients and tailored to each woman's level of risk, balance of risk and benefits, and personal preferences.
Strategies for Women with Average Risk
For women with average risk, the emphasis is on healthy lifestyle habits.
Regular physical activity may be especially important to risk reduction. According to a 2011 review of epidemiological studies, a 25% average risk reduction was reported for physically active women (as compared to the least active women). This is likely due to the impact of exercise on reducing levels of estrogen serums, insulin and insulin growth factor-1, rather than through the influence of physical activity body weight alone.10 The American Cancer Society recommends that women avoid alcohol. The impact of alcohol on risk is dose-dependent, so that even a reduction in the amount of alcohol consumed can lower risk. Additionally, women who drink alcohol may wish to consider a daily multivitamin that includes folic acid as folic acid intake may weaken the effect of alcohol on breast cancer.35
Women should also maintain a healthy body weight, particularly post-menopause,and consider a low-fat diet. Although study findings on the relationship between dietary fat and breast cancer are inconclusive, at minimum, a low-fat diet can help to reduce risk indirectly by helping to prevent obesity.
Strategies for Reducing Breast Cancer Risk:
maintain a healthy body weight
lower dietary fat
breast feed for longer periods
avoid or minimize the duration of HRT
consider minimizing night shift work
Patients wishing to decrease their risk of breast cancer should also avoid smoking. While the research in this area is inconclusive, most recent studies appear to suggest a linkage, and smoking cessation leads to other important health benefits as well.
Women who give birth might wish to consider lengthening the duration of breastfeeding. An analysis of data from forty-seven epidemiologic studies estimated an approximate 4% reduction in relative risk for every twelve months of breastfeeding.10
Avoiding or minimizing the duration of hormone replacement therapy after menopause will keep a woman from increasing her risk. For women who choose to use HRT, the U.S. Food and Drug Administration currently recommends the shortest time and at the lowest dose possible.19
Finally, night-shift work appears to be related to slight elevation in breast cancer risk. Women may wish to avoid or minimize working night shifts.10
Patients who modify their lifestyle choices toward reducing their risk of breast cancer will be taking constructive steps toward better overall health. The risk of breast cancer cannot, however, be completely eliminated for any woman. Other than lifestyle changes, the most important action a woman can take to decrease her chances of dying from breast cancer is to follow early detection guidelines. The earlier breast cancer is found, the better the chances for successful treatment.10
Strategies for Women at Increased
For women with increased risk, additional risk reduction strategies should be considered. At present, these strategies include:
the use of additional imaging tests
chemoprevention (e.g., tamoxifen)
for women with a strong family history or known genetic predisposition, prophylactic mastectomy
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National Cancer Institute. (2008, April 30). Alcohol and breast cancer risk: New findings. Retrieved from: http://www.cancer.gov/cancertopics/causes/breast/alcoholuse0408
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