Moving forward with breast cancer prevention

Accelerating the Pace of Cancer Prevention- Right Now

As a nation, we underinvest in prevention and fail to implement strategies that ensure all population groups equitably share in the return on investment in prevention research and the benefits of prevention effectiveness. There is significant evidence indicating that by applying knowledge that we already have to reduce tobacco, inactivity, and obesity (known modifiable causes of cancer), we can prevent more than 50% of cancers. Vaccination against HPV, aspirin and selective estrogen receptor modulators, and screening programs further reduce risk. Evidence-based prevention strategies are inconsistently implemented across the United States. Substantial variation across States indicates that there is much room for improvement in implementation of prevention. Implementation science applies innovative approaches to identifying, understanding, and developing strategies for overcoming barriers to the adoption, adaptation, integration, scale-up, and sustainability of evidence-based interventions, tools, policies, and guidelines that will prevent cancer through application of evidence-based interventions. When we get implementation of prevention programs right and at scale, we achieve substantial population benefits. Although many efforts are underway to maximize our knowledge about the causes and treatments of cancer, we can achieve reductions in the cancer burden right now by doing what we already know. The time to start is now. Cancer Prev Res; 11(4); 171-84. ©2018 AACR.

Priorities for the primary prevention of breast cancer

Despite recent calls to intensify the search for new risk factors for breast cancer, acting on information that we already have could prevent thousands of cases each year. This article reviews breast cancer primary prevention strategies that are applicable to all women, discusses the underutilization of chemoprevention in high-risk women, highlights the additional advances that could be made by including young women in prevention efforts, and comments on how the molecular heterogeneity of breast cancer affects prevention research and strategies.

Suitable trial designs and cohorts for preventive breast cancer agents

Effective chemoprevention of oestrogen receptor (ER)-positive breast cancer has been shown convincingly using several selective ER modulators and the aromatase inhibitor exemestane. Although these agents are well tolerated and the numbers needed-to-treat in the prevention setting are similar to other established preventive interventions, uptake has been poor in clinical practice because of difficulties in visualizing risk, predicting individual outcomes and measuring treatment benefit. In addition, new agents targeting ER-negative breast cancer are urgently needed. The development of new agents is hampered by the lack of suitable biomarkers and targets, as well as regulatory and financial considerations. Establishing breast cancer chemoprevention in standard clinical practice will require advances in many different fields, including biomarker research, the development of more powerful tools to predict and communicate the risks and benefits of treatments and establishing innovative trial designs. Furthermore, changes in regulatory procedures could reduce the size and cost of trials needed in the prevention setting. Identification of biomarkers for risk and efficacy that are easily accessible, such as blood-based biomarkers, will be key to future chemoprevention strategies.

Applying what we know to accelerate cancer prevention

More than half of the cancer occurring today is preventable by applying knowledge that we already have. Tobacco, obesity, and physical inactivity are the modifiable causes of cancer that generate the most disease. Cancer burden can be reduced by alterations in individual and population behaviors and by public health efforts as long as these changes are driven by sound scientific knowledge and social commitment to change. The obstacles to these efforts are societal and arise from the organization of institutions, including academia, and in the habits of daily life. To achieve maximal possible cancer prevention, we will need better ways to implement what we know and improved infrastructure that will better incentivize and support transdisciplinary, multilevel research and successful intervention.

Preventability of cancer: the relative contributions of biologic and social and physical environmental determinants of cancer mortality

Whereas models of cancer disparities and variation in cancer burden within population groups now specify multiple levels of action from biologic processes to individual risk factors and social and physical contextual factors, approaches to estimating the preventable proportion of cancer use more traditional direct models often from single exposures to cancer at specific organ sites. These approaches are reviewed, and the strengths and limitations are presented. The need for additional multilevel data and approaches to estimation of preventability are identified. International or regional variation in cancer may offer the most integrated exposure assessment over the life course. For the four leading cancers, which account for 50% of incidence and mortality, biologic, social, and physical environments play differing roles in etiology and potential prevention. Better understanding of the interactions and contributions across these levels will help refine prevention strategies.

Prevention trials: their place in how we understand the value of prevention strategies

Several key factors bear on the interpretation of prevention trials and observational studies that inform prevention strategies. These factors include the underlying disease process and aspects of the intervention: sustainability of behavior change, the time course of the intervention within the disease process, dose and duration of exposure needed to effect risk reduction, durability of the impact of intervention, and methodological problems in implementing and interpreting randomized trials and observational studies to evaluate prevention strategies. The question asked through an intent-to-treat analysis of a randomized controlled trial (RCT) differs from that in the observational setting. Furthermore, the long duration necessary to conduct prevention trials and the resulting lack of adherence to therapy can bias results toward the null. A broader range of approaches to evaluate prevention interventions and programs with improved knowledge synthesis and translation to public health practice will speed our progress toward achieving public health and prevention of chronic diseases.

A randomized controlled trial of calcium plus vitamin D supplementation and risk of benign proliferative breast disease

Experimental evidence provides strong support for anti-carcinogenic effects of calcium and vitamin D with respect to breast cancer. Observational epidemiologic data also provide some support for inverse associations with risk. We tested the effect of calcium plus vitamin D supplementation on risk of benign proliferative breast disease, a condition which is associated with increased risk of breast cancer. We used the Women's Health Initiative randomized controlled trial. The 36,282 participants were randomized either to 500 mg of elemental calcium as calcium carbonate plus 200 IU of vitamin D(3) (GlaxoSmithKline) twice daily (n = 18,176) or to placebo (n = 18,106). Regular mammograms and clinical breast exams were performed. We identified women who had had a biopsy for benign breast disease and subjected histologic sections from the biopsies to standardized review. After an average follow-up period of 6.8 years, 915 incident cases of benign proliferative breast disease had been ascertained, with 450 in the intervention group and 465 in the placebo group. Calcium plus vitamin D supplementation was not associated with altered risk of benign proliferative breast disease overall (hazard ratio = 0.99, 95% confidence interval = 0.86-1.13), or by histologic subtype. Risk varied significantly by levels of age at baseline, but not by levels of other variables. Daily use of 1,000 mg of elemental calcium as calcium carbonate plus 400 IU of vitamin D(3) for almost 7 years by postmenopausal women did not alter the overall risk of benign proliferative breast disease.