Breast Cancer and the Environment A Life Course Approach (2012) / Chapter Skim
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6 Opportunities for Action to Reduce Environmental Risks for Breast Cancer
6 Opportunities for Action to Reduce Environmental Risks for Breast Cancer
Pages 283-324
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From page 283... ...
Will reducing or eliminating exposure in adulthood reduce a risk that has accrued from exposure at younger ages? Will the presence or absence of other risk factors for breast cancer influence the likely benefit or harm from a change in exposure to a given risk factor?
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From page 284... ...
Depending on these values, it is possible that a comparative risk assessment would show that switching from the contaminated groundwater supply to the uncontaminated but disinfected surface water supply actually increased, rather than decreased, potential cancer risks to the exposed population. This example, however, also illustrates the challenges in assessing tradeoffs in population- and individual-level risks and benefits.
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From page 285... ...
Challenges in Public Health Policy Aimed at Risk Reduction A significant challenge -- relevant to the discussion of environmental risk factors for breast cancer and frequently faced by regulators of environmental pollutants and public health officials -- is a lack of information about the nature of the effects of many exposures on risks for breast cancer. Chapter 4 reviewed the diverse challenges in trying to generate and interpret relevant information.
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From page 286... ...
and other environmental regulatory agency scientists often assume that cancer risks in a population are simply the sum of risks estimated for each individual chemical in the absence of data on risks of co-exposures. In practice, this means that one might be confident that a lifetime of exposure to a single chemical that causes a theoretical increase in cancer risk of 1 additional case per 1 million exposed people is essentially lost in the background and that the risk from that exposure may be considered minimal.
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From page 287... ...
Perhaps most salient is the difficulty in assessing whether reduction or elimination of an exposure will alter long-term risk of breast cancer, and if so, by how much. EVIDENCE-BASED OPPORTUNITIES FOR ACTION TO REDUCE RISK Identifying evidence-based opportunities for action to reduce risk of breast cancer depends, ideally, on a convergence of several elements, including • sufficient evidence to demonstrate that a specific factor is associated with increasing or decreasing breast cancer risk; • a means by which to modify exposure to the risk factor; • an understanding of whether effective changes can be made by an individual or would require instead, or in addition, changes at governmental, social, or cultural levels; • evidence that a specific action to modify exposure will result in the desired impact on breast cancer risk, the characteristics of women who could be expected to benefit, and when the intervention needs to occur; and • awareness of the trade-offs (potentially as yet unrecognized)
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From page 288... ...
Whereas evidence indicates that greater weight is associated with an increased risk for breast cancer for postmenopausal women, it also indicates that greater weight is associated with a lower risk of breast cancer for premenopausal women (WCRF/AICR, 2007)
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Younger women, however, tend to have ER– forms of breast cancer, as do women who have strong inherited susceptibility to breast cancer, such as carrying a mutation in BRCA1. All women should know their personal risk factors for breast cancer and seek clinical guidance from their health care providers regarding their breast cancer risk and how to modify it.
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290 BREAST CANCER AND THE ENVIRONMENT TABLE 6-1 Summary of Committee Assessment of Opportunities for Actions by Women That May Reduce Risk of Breast Cancer Modification of Exposure Strength of Evidence That Personal Requires Opportunity for Exposure Is Associated Action Action with Breast Cancer Riska Action Possible by Others Avoid +++ Yes Yes inappropriate medical radiation exposured Avoid combination +++ Yes Confer with physician menopausal hormone therapy, unless medically appropriatee Avoid or end active + Yes Others can facilitate smoking Avoid passive (no committee consensus) Varies Yes smoking Limit or ++ Yes Others can facilitate eliminate alcohol consumption – –f Maintain or Yes Others can facilitate increase physical activity Maintain healthy +++ Yes Others can facilitate weight or reduce overweight or obesity to reduce postmenopausal risk
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cardiovascular disease No known benefit of high alcohol consumption All ages No ? Likely to reduce risk for cardiovascular disease, diabetes May increase risk for injury Unclear No ER+?
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Studies have not been done that provide evidence that a specific form of physical activity is optimal for reducing breast cancer risk. cThe committee's comments on other benefits or risks highlight major considerations, but are not intended to be exhaustive.
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These contraceptives are associated with long-term risk reduction for ovarian and endometrial cancer. fReflects reduced risk of breast cancer associated with greater physical activity.
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From page 294... ...
to standardize and minimize radiation doses received from mammography, but the United States has no federal oversight for other imaging examinations and no guidelines on optimal doses. Evidence shows that physicians are insufficiently informed about radiation doses or the cancer risks attributable to the medical imaging they order (Lee et al., 2004)
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From page 295... ...
Patients and Families: Individuals can question health providers specifically about what is known regarding the health benefits and harms associated with proposed diagnostic tests that involve exposure to ionizing radiation. They can request information about the relative doses of radiation associated with each type of procedure they undergo.
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, which included a randomized clinical trial to assess the health effects of combination hormone therapy (i.e., a product with estrogen and progestin) , demonstrated an increased risk of breast cancer among postmenopausal women taking combination hormone therapy (Writing Group for the Women's Health Initiative Investigators, 2002)
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. The USPSTF guidelines recommend against the routine use of combination hormone therapy for the prevention of chronic conditions because the increased risks of breast cancer, stroke, and other conditions are considered to outweigh the potential benefits of reduced risks for fractures and colorectal cancer.
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Because observational studies have consistently shown an increased risk of breast cancer among women with higher endogenous estrogen and androgen serum concentrations (Key et al., 2002; Hankinson, 2005–2006) , there is little to suggest that use of bioidentical hormones would be a safe alternative to other forms of hormone therapy.
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From page 299... ...
Other medications not currently approved for use for breast cancer risk reduction are also being evaluated. One category of drugs is aromatase inhibitors, designed to inhibit the conversion of androgen to estrogen, and early results from a study of the aromatase inhibitor exemestane show a reduced risk of breast cancer among high-risk women (Goss et al., 2011)
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, and stroke. Benefits for menopausal women, in addition to breast cancer risk reduction, include lower fracture risks.
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Efforts can also be made to encourage smoke-free homes and cars. Given that initiation of smoking generally occurs in adolescence or earlier, the evidence linking smoking before a first full-term pregnancy with increased risk of breast cancer underscores the need for effective programs geared towards smoking prevention in preteen and teenage girls.
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From page 302... ...
However, with the lack of evidence regarding the impact on breast cancer risk of changes in consumption and the evidence supporting beneficial effects of moderate alcohol consumption related to cardiovascular disease, the merits of restricting or eliminating moderate alcohol consumption as a breast cancer risk reduction strategy are hard to judge for individual women.
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. Additional research is needed to clarify the type of activity, the amount, and the timing of physical activity over the life course that can produce a reduction of breast cancer risk.
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It also appears that the association of greater weight and adult weight gain with increased postmenopausal breast cancer risk is dominated by the experience of white women and may not hold for African American women (Palmer et al., 2007)
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While recognizing potential hazards, the committee did not have the capacity to estimate breast cancer risks at these low doses because the information necessary to do so is insufficient. Because these chemicals are recognized carcinogens (NTP, 2011)
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The committee concluded that avoiding exposure to either hair dyes or non-ionizing radiation has little potential to contribute to a substantial reduction in breast cancer risk for individuals or the population. For certain other compounds, such as dioxins, polychlorinated biphenyls (PCBs)
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From page 307... ...
Determining the sustainability of such changes, their acceptability to a broader population, and whether such reductions would actually decrease breast cancer risk would require further investigation. The committee recognizes, however, that existing data indicate that BPA and some other substances may be hazards to human health and may well warrant consideration of actions by regulatory agencies that are aimed at reducing future population-based exposures.
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, or for improvement of athletic performance or weight loss, have not been tested for safety or effectiveness. Interest in such supplements could be amplified by messages that hormone therapies, physical inactivity, and overweight are risk factors for breast cancer.
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Here, the committee offers some perspective on levels of breast cancer risks, interrelationships among risk factors, and what we know about risk reduction.
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The Breast Cancer Risk Assessment Tool (Gail et al., 1989; NCI, 2011a) and the Tyrer-Cuzick breast cancer risk assessment model (Tyrer et
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al., 2004) are designed to generate estimates of absolute risk for individuals in conjunction with absolute risk estimates for the general population as a reference.7 The Breast Cancer Risk Assessment Tool (NCI, 2011a)
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It is helpful for researchers and policy makers in assessing possible opportunities to reduce disease burden through public health interventions that target specific modifiable risk factors in the population as a whole, but has limited applicability for an individual. For instance, the PAR can be used to estimate how many cases of breast cancer might be prevented if half of the women offered unnecessarily high levels of medical radiation were able to avoid those high levels, or if an additional 25 percent of women did not gain weight and become obese or overweight by the time they reached menopause.
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For example, if combination hormone therapy is widely used in a study population, its PAR would tend to higher than the PAR for hormone therapy in a study population with relatively limited use. PARs should at best be viewed as ballpark estimates of potential impact on breast cancer risk on a population level, under the assumption that the associations are causal.
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From page 314... ...
For a limited set of other risk factors, evidence suggests that action can be taken in ways that that have the potential to reduce risk for breast cancer for many women: eliminating unnecessary medical radiation throughout life, avoiding use of postmenopausal hormone therapy, avoiding active and passive smoking, reducing alcohol consumption, increasing physical activity, and minimizing weight gain. Chemoprevention may be an appropriate choice for some women.
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, or they may be health related (e.g., moderate alcohol consumption increases breast cancer risk, but it may reduce risk of heart disease; tamoxifen reduces risk for breast cancer but increases risk for stroke and endometrial cancer)
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2008. Menopausal hormone therapy and breast cancer risk in the NIH–AARP Diet and Health Study Cohort.
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2009. Canadian expert panel on tobacco smoke and breast cancer risk.
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1992. Increased risk of breast cancer with alcohol consumption in postmenopausal women.
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2004. Patterns of alcohol consumption and breast cancer risk in the California Teachers Study cohort.
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Trends in attributable risk for modifiable breast cancer risk factors in Canadian women. Can J Public Health 101(5)
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2011. Risk factor modification and projections of absolute breast cancer risk.
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2010. Cancer risks after radiation exposure in middle age.
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2011. Physical activity and cancer prevention: A systematic review of clinical trials.
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