Association between body mass index and breast cancer risk: evidence based on a dose-response meta-analysis

Breast cancer chemoprevention: An update on current practice and opportunities for primary care physicians

Several risk assessment models have been validated for the estimation of risk of breast cancer in women. Chemoprevention through hormonal therapy is an effective way to reduce the incidence of breast cancer in women with high risk. Selective estrogen receptor modulators, tamoxifen and raloxifene, are approved for this indication by the United States Food and Drug Administration, and aromatase inhibitors have also shown promise in recent studies. These medications are generally well tolerated, except for reported increased rates of fractures and venous thromboembolic events. Despite strong recommendations from several regulatory bodies, advocacy for chemoprevention has been inadequate in practice, more so among the primary care physicians. Studies have identified several barriers in physicians, patients, and the system, contributing to this problem. Lack of knowledge about risk assessment models and chemoprevention options preclude physicians from prescribing these medications with confidence. Fear of potential adverse events, confusion regarding the purpose of the therapy, and need for continued adherence for five years are among the principal reasons for reduced chemoprevention uptake and early discontinuation among patients. Multifaceted interventions directed at education and training of health care professionals, proper counseling of women at high risk, and promotion of the development of improved medications might help ensure better chemoprevention uptake in the target population.

Prospective Analysis of Food Consumption and Nutritional Status and the Impact on the Dietary Inflammatory Index in Women with Breast Cancer during Chemotherapy

Considering the implications of adverse effects of chemotherapy (CT) and the potential impact of diet on patients’ recovery, this study aimed to prospectively evaluate the association between the consumption of food groups, patients’ Dietary Inflammatory Index (DII^®) scores, and their nutritional status. Anthropometric and dietary assessments of 55 women with breast cancer (BC) were performed at three time points. T0 is the time point after the first CT cycle, T1 is the time point after the intermediate CT cycle, and T2 is the time point after the last CT cycle. We identified a significant increase in weight, body mass index, and waist circumference during CT. Consumption of poultry and eggs was higher in T1 when compared to T2, while consumption of total fruit and total vegetables was higher at T0 compared to T1 and T2. The diet became more pro-inflammatory over the course of treatment (X²₍₂₎ = 61.127), and was related to higher abdominal adiposity. Total fruit (T0: R² = 0.208, T1: R² = 0.095, T2: R² = 0.120) and total vegetable consumption (T0: R² = 0.284, T1: R² = 0.365, T2: R² = 0.580) predicted DII^® change at the three-time points. Meanwhile, consumption of total grains was significantly associated only with T1 (R² = 0.084) and T2 (R² = 0.118), and consumption of simple sugars was significantly associated only with T0 (R² = 0.137) and T1 (R² = 0.126). Changes in food consumption led to an increase in the inflammatory profile of the diet, suggesting the necessity to improve the guidelines during and after CT. These results reinforce the need to promote healthier eating practices in concert with maintaining a healthy nutritional status in women with BC treated with CT.

Association of metabolic NCD risk factors with oral, breast and cervical precancers and cancers in India

OBJECTIVE

To find an association between metabolic non-communicable disease (NCD) risk factors (high blood pressure (BP), high random blood sugar (RBS) and overweight /obesity) and oral, breast, cervical cancers/precancerous or potentially malignant conditions.

DESIGN

This is an observational study using convenience sampling. The participants were screened through opportunistic or population-based screening.

SETTING

The study was conducted at a health promotion clinic (HPC) located in Northern India under the Indian Council of Medical Research. HPC is a screening clinic where screening is done for hypertension (HT), diabetes mellitus (DM), obesity, and oral, breast and cervical cancers. The study was conducted between December 2016 and January 2019.

PARTICIPANT

The number of participants screened was 8352 (6712 women and 1640 men). All consenting men and women above 18 years were included. All participants were screened for oral cancer, DM, HT and obesity. All women were also screened for breast and cervical cancers. Cervical screening was done for non-pregnant women 21 years and above with history of sexual activity.

RESULT

Oral potentially malignant disease (OPMD) was the most prevalent, followed by breast cancer, oral cancer, cervical cancer and cervical precancer. High RBS had a strong association with oral cancer (OR=2.29, 95% CI 1.09 to 4.82, p=0.03) and breast cancer (OR=1.95, 95% CI 1.01 to 3.76, p=0.05). High BP had a strong association with breast cancer (OR=2.50, 95% CI 1.43 to 4.35, p<0.0001). An inverse association was noted between oral cancer and overweight/obesity (OR=0.20, 95% CI 0.08 to 0.48, p<0.0001). Current tobacco use was strongly associated with oral cancer (OR=6.51, 95% CI 3.63 to 11.67, p<0.0001) and OPMD (OR=9.82, 95% CI 8.13 to 11.86, p<0.0001). No association was elicited between the metabolic NCD risk factors and cervical cancer/precancer.

CONCLUSIONS

The study reaffirms that NCD metabolic risk factors determine oral and breast cancers. Besides NCD risk factors, current tobacco use was a strong determinant of OPMD and oral cancer. Hence, primary and primordial prevention measures to control NCD metabolic risk factors and tobacco use should move along with secondary prevention of breast and oral cancers.

Causal relationships between obesity and the leading causes of death in women and men

Obesity traits are causally implicated with risk of cardiometabolic diseases. It remains unclear whether there are similar causal effects of obesity traits on other non-communicable diseases. Also, it is largely unexplored whether there are any sex-specific differences in the causal effects of obesity traits on cardiometabolic diseases and other leading causes of death. We constructed sex-specific genetic risk scores (GRS) for three obesity traits; body mass index (BMI), waist-hip ratio (WHR), and WHR adjusted for BMI, including 565, 324, and 337 genetic variants, respectively. These GRSs were then used as instrumental variables to assess associations between the obesity traits and leading causes of mortality in the UK Biobank using Mendelian randomization. We also investigated associations with potential mediators, including smoking, glycemic and blood pressure traits. Sex-differences were subsequently assessed by Cochran's Q-test (Phet). A Mendelian randomization analysis of 228,466 women and 195,041 men showed that obesity causes coronary artery disease, stroke (particularly ischemic), chronic obstructive pulmonary disease, lung cancer, type 2 and 1 diabetes mellitus, non-alcoholic fatty liver disease, chronic liver disease, and acute and chronic renal failure. Higher BMI led to higher risk of type 2 diabetes in women than in men (Phet = 1.4×10-5). Waist-hip-ratio led to a higher risk of chronic obstructive pulmonary disease (Phet = 3.7×10-6) and higher risk of chronic renal failure (Phet = 1.0×10-4) in men than women. Obesity traits have an etiological role in the majority of the leading global causes of death. Sex differences exist in the effects of obesity traits on risk of type 2 diabetes, chronic obstructive pulmonary disease, and renal failure, which may have downstream implications for public health.

Obesity as potential breast cancer risk factor for postmenopausal women

Breast cancer is the second highest prevalent cancer globally after lung cancer with 2.09 million cases during 2018. Adults about 1.9 billion were overweight and over 650 million out of these were obese during 2016. There is a significant relationship between breast cancer risk and obesity. Premature menopause and premenopausal obesity diminish the risk whereas postmenopausal obesity amplifies the risk, because adipose tissue acts as the major reservoir for estrogen biosynthesis after menopause. Lofty estrogen levels in serum along with enhanced peripheral site production of estrogen have been viewed as major reasons of developing breast cancer in overweight postmenopausal women. This review explains body fat as a peripheral site for estrogen biosynthesis, estrogen exposure affecting body fat distribution, and the mechanism of estrogen production from body fats.

The Many Faces of Obesity and Its Influence on Breast Cancer Risk

Obesity is associated with increased risk of breast and other cancers. However, the complexity of the underlying mechanisms, together with the interplay of diet and physical activity—contributing to energy balance—and the role of adipose tissue, pose challenges to our understanding of the basis of this increased risk. Epidemiologic studies have documented a higher obesity prevalence in US black women compared to white women. Elucidation of the contribution of potential biological differences among racially distinct groups to their differences in breast cancer (BC) risk and mortality have been topics of considerable interest in recent years. The racial and ethnic variation in body fat distribution may account for at least part of the differences in breast cancer rates in these populations. Yet, while black women exhibit higher rates of obesity compared to white women, this does not translate directly into higher rates of BC. In fact, overall, BC in black women occurs with a lower incidence than BC in white women. Obesity is a known risk factor for postmenopausal breast cancer, and growing evidence suggests that abdominal obesity, also known as central obesity, may increase risk for triple negative breast cancer, which is more common in premenopausal women. The positive association of postmenopausal BC risk and specifically estrogen receptor (ER)-positive BC, is presumably due largely to accumulation of estrogen in the adipose tissue of the breast and other tissues. Of the two main types of adipose tissue—subcutaneous and visceral—visceral adipocytes are more active metabolically. Such adipose tissue harbors multiple molecular entities that promote carcinogenesis: endocrine molecules/hormones, immunologic factors, inflammatory cytokines, metabolic alterations, and other components of the microenvironment. Expression of these culpable entities is largely regulated by epigenetic mechanisms. The interrelationship between these entities and drivers of epigenetic alteration are critical to the regulation of pathways connecting obesity and cancer risk. Initiatives to counteract the carcinogenic effects of obesity have primarily involved modulation of energy balance by diet. However, targeting of specific molecular abnormalities characterizing adiposity offers an alternative approach to preventing cancer. Our goal in this review is to first discuss the major mechanisms contributing to the obesity-breast cancer link. We will also consider race, specifically black/white differences, as they relate to the association of obesity with breast cancer risk. Then we will enumerate strategies targeting these mechanisms to reduce BC risk, in large part by way of dietary interventions with potential to mitigate the cancer-promoting components of adiposity.

The genetic interplay between body mass index, breast size and breast cancer risk: a Mendelian randomization analysis

BACKGROUND

Evidence linking breast size to breast cancer risk has been inconsistent, and its interpretation is often hampered by confounding factors such as body mass index (BMI). Here, we used linkage disequilibrium score regression and two-sample Mendelian randomization (MR) to examine the genetic associations between BMI, breast size and breast cancer risk.

METHODS

Summary-level genotype data from 23andMe, Inc (breast size, n = 33 790), the Breast Cancer Association Consortium (breast cancer risk, n = 228 951) and the Genetic Investigation of ANthropometric Traits (BMI, n = 183 507) were used for our analyses. In assessing causal relationships, four complementary MR techniques [inverse variance weighted (IVW), weighted median, weighted mode and MR-Egger regression] were used to test the robustness of the results.

RESULTS

The genetic correlation (rg) estimated between BMI and breast size was high (rg = 0.50, P = 3.89x10-43). All MR methods provided consistent evidence that higher genetically predicted BMI was associated with larger breast size [odds ratio (ORIVW): 2.06 (1.80-2.35), P = 1.38x10-26] and lower overall breast cancer risk [ORIVW: 0.81 (0.74-0.89), P = 9.44x10-6]. No evidence of a relationship between genetically predicted breast size and breast cancer risk was found except when using the weighted median and weighted mode methods, and only with oestrogen receptor (ER)-negative risk. There was no evidence of reverse causality in any of the analyses conducted (P > 0.050).

CONCLUSION

Our findings indicate a potential positive causal association between BMI and breast size and a potential negative causal association between BMI and breast cancer risk. We found no clear evidence for a direct relationship between breast size and breast cancer risk.

Prevalence of breast cancer-related risk factors in underweight premenopausal women: the Korea National Health and Nutrition Examination Survey IV-VI

PURPOSE

This study aimed to examine the prevalence and trends of breast cancer-related risk factors and characteristics in premenopausal underweight Korean women according to birth year cohort.

METHODS

Socioeconomic and breast cancer-related risk factors were investigated in 13,415 premenopausal women using nationwide cross-sectional surveys performed between 2007 and 2015. Underweight was defined as body mass index < 18.5 kg/m². Multivariable models were created using complex sample procedures.

RESULTS

Underweight women comprised 9.5% of the sample. Compared with those who were obese or of normal weight, underweight women were characterized by younger age, higher rate of metropolitan residence, higher economic status, more education, higher rates of non-manual employment and unmarried status, lower rate of early menarche, higher rates of nulliparity, lower parity, alcohol consumption, and never having breastfed, and lower levels of high physical activity. Multivariable analysis showed that underweight women had a significantly lower rate of early menarche, lower parity, higher nulliparity, older age at first delivery, and lower levels of high physical activity compared to premenopausal women with normal weight. These trends were more apparent among women born in recent years.

CONCLUSIONS

Underweight Korean premenopausal women exhibit distinctive features associated with an increased risk of breast cancer, except for a lower rate of early menarche. These associations were prominent in recent generations. Assessment of the association between underweight and premenopausal breast cancer risk should focus on promoting healthy lifestyles to reduce breast cancer risk.