Nutritional factors, physical activity, and breast cancer by hormonal receptor status

Animal foods and postmenopausal breast cancer risk: a prospective cohort study

The role of diet on breast cancer risk is not well elucidated but animal food sources may play a role through, for example, the pathway of the insulin-like growth factor 1 system or cholesterol metabolism. The aim of this study was to evaluate the association between animal foods and the risk of postmenopausal breast cancer. This study was embedded in the Rotterdam Study, a population-based prospective cohort study of subjects aged 55 years and over (61 % female). Dietary intake of different animal foods was assessed at baseline using a validated FFQ and adjusted for energy intake using the residual method. We performed Cox proportional hazards modelling to analyse the association between the intake of the different food sources and breast cancer risk after adjustment for socio-demographic, lifestyle and metabolic factors. During a median follow-up of 17 years, we identified 199 cases of breast cancer (6·2 %) among 3209 women. After adjustment for multiple confounders, no consistent association was found between the intake of red meat intake, poultry, fish or dairy products and breast cancer risk. However, we found that egg intake was significantly associated with a higher risk of breast cancer (hazard ratioQ4 v. Q1: 1·83; 95 % CI 1·20, 2·79; Ptrend=0·01). In conclusion, this study found that dietary egg intake but no other animal foods was associated with a higher risk of postmenopausal breast cancer. Further research on the potential mechanisms underlying this association is warranted.

Physical Activity and Weight Loss Reduce the Risk of Breast Cancer: A Meta-analysis of 139 Prospective and Retrospective Studies

BACKGROUND

Physical activity and weight loss have been shown to reduce breast cancer incidence in numerous observational studies. The aim of this meta-analysis was to assess the effect of both physical activity and weight loss on breast cancer incidence. Specifically, we aimed to complete subgroup analyses by the intensity of physical activity and menopausal status at breast cancer diagnosis to further elucidate the relationship between physical activity, weight loss, and breast cancer incidence.

MATERIALS AND METHODS

Studies were obtained from a database search of MEDLINE, EMBASE, PubMed, Current Contents Connect, and Google Scholar through November 5, 2017. A random-effects model was used for pooled data.

RESULTS

There were 139 studies included in the meta-analysis, including 236,955 cases and 3,963,367 controls. Physical activity significantly reduced the risk of breast cancer (odds ratio [OR], 0.78; 95% confidence interval [CI], 0.76-0.81; P < .001), with high-intensity physical activity being slightly more protective (OR, 0.73; 95% CI, 0.65-0.81; P < .001) than low-intensity exercise (OR, 0.79; 95% CI, 0.72-0.86; P < .001). The effect size for general exercise was similar in both premenopausal (OR, 0.79; 95% CI, 0.73-0.87; P < .001) and postmenopausal (OR, 0.82; 95% CI, 0.78-0.86; P < .001) women. Additionally, weight loss reduced the risk of breast cancer incidence (OR, 0.82; 95% CI, 0.67-0.97).

CONCLUSION

Physical activity and weight loss significantly reduce the risk of breast cancer, irrespective of the timing and intensity of the exercise.

Dietary Patterns for Women With Triple-negative Breast Cancer and Dense Breasts

Triple-negative breast cancer (TNBC) is a common subtype of breast cancer among women with dense breasts and is associated with a poor prognosis. Diet is a modifiable risk factor for breast cancer, but the association between the risk of TNBC and diet has not been studied. The present study investigated the hypothesis that a healthy dietary pattern was negatively associated with risk of TNBC in women with dense breasts (density types 3 and 4). After total mastectomy or breast conserving surgery, patients with TNBC (n = 38) and non-TNBC (n = 178) were recruited. The risk of TNBC was negatively associated with a healthy dietary pattern involving consumption of seafood and vegetables, and positively associated with a dietary pattern of consuming grains, meats, and eggs. Additionally, intake of animal fat, eggs, and meat was positively associated with the risk of TNBC, but intake of vegetable fats, nuts, and vegetables showed a negative association. Patients with TNBC had higher proportion of obesity or abdominal obesity than those with non-TNBC. The present study is the first to show a negative association between risk of TNBC and a healthy dietary pattern in women with dense breasts and suggests the importance of diet in the prevention of TNBC.

Recreational physical activity and risk of triple negative breast cancer in the California Teachers Study

BACKGROUND

Evidence has accumulated showing that recreational physical activity reduces breast cancer risk. However, it is unclear whether risk reduction pertains to specific receptor-defined subtypes. Moreover, few studies have examined whether changes in the amount of recreational physical activity during adulthood influence breast cancer risk.

METHODS

A total of 108,907 women, ages 22 to 79 years with no history of breast cancer when joining the California Teachers Study in 1995-1996, completed a baseline questionnaire and were eligible for the study. Through 2012, 5882 women were diagnosed with invasive breast cancer. Breast cancer subtypes were defined by the expression status of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Multivariable Cox proportional hazards models provided adjusted hazard ratios (HRs) and 95 % confidence intervals (CIs) for breast cancer overall and ER/PR/HER2-defined subtypes associated with long-term (from high school through age 54 or age at cohort entry, whichever was younger) and baseline (during 3 years prior to baseline) recreational physical activity. Among women who also completed a follow-up questionnaire at 10 years after baseline in 2005-2008 (54,686 women, 1406 with invasive breast cancer), risk associated with changes in the amount of recreational physical activity from baseline to the 10-year follow-up (during 3 years prior to the 10-year follow-up) was determined.

RESULTS

Both long-term and baseline strenuous recreational physical activity were inversely associated with risk of invasive breast cancer (P trend ≤0.03). The observed associations were mainly confined to women with triple negative breast cancer (TNBC, ER-/PR-/HER2-, P trend ≤0.02) or luminal A-like subtype (ER+ or PR+ plus HER2-) who were former users of menopausal hormone therapy at baseline (P trend = 0.02, P homogeneity of trends ≤0.03). Moreover, women who consistently engaged in the highest level (≥3.51 h/wk/y) of strenuous recreational physical activity between baseline and 10-year follow-up had the lowest risk of breast cancer (HR = 0.71, 95 % CI = 0.52-0.98) when compared to those who were consistently low (≤0.50 h/wk/y).

CONCLUSIONS

Strenuous recreational physical activity is associated with lower breast cancer risk, especially TNBC. The benefit may be maximized by consistently engaging in high-intensity recreational physical activity during adulthood.

Plasma phospholipids fatty acids, dietary fatty acids, and breast cancer risk

PURPOSE

This study prospectively investigates associations between fatty acids assessed in plasma phospholipids (PPL) and diet, and breast cancer risk, including subgroups defined by hormone receptor status.

METHODS

We performed a case-cohort analysis within the Melbourne Collaborative Cohort Study using a random sample of 2,021 women and 470 breast cancer cases. At baseline, fatty acids were assessed in PPL and estimated from diet using a 121-item food frequency questionnaire. Hazard ratios (HR) and 95 % confidence intervals (CI) were estimated using Cox regression.

RESULTS

Breast cancer risk was positively associated with %PPL saturated fatty acids (SFA); HRQ5vsQ1 = 1.64 (95 % CI 1.17-2.30); p trend = 0.004. Positive associations were found for ER+ or PR+ tumors for %PPL SFA and palmitic acid and for ER-/PR- tumors for %PPL n-6 polyunsaturated fatty acid (PUFA), TFA, TFA 16:1, and TFA 18:1n-7 (all p homogeneity <0.05). Breast cancer risk was inversely associated with dietary docosapentaenoic acid (DPA); HRQ5vsQ1 = 0.57 (95 % CI 0.40-0.82); p trend = 0.001 [with similar inverse associations observed for dietary docosahexaenoic (DHA) and eicosapentaenoic acid (EPA)] and positively associated with dietary n-6:n-3 PUFA. Inverse associations for ER-/PR- tumors were found for dietary dihomo-γ-linolenic acid (DGLA) for older women (p homogeneity = 0.04).

CONCLUSIONS

Breast cancer risk was positively associated with %PPL SFA and the ratio of dietary n-6 to n-3 PUFA and inversely associated with dietary long-chain n-3 PUFA intake. Some associations between fatty acids and breast cancer varied by age and tumor phenotype defined by hormone receptor status. Increased intake of fish and other foods rich in long-chain n-3 PUFAs and reduced n-6 PUFA intake might reduce breast cancer risk.

A prospective study of occupational physical activity and breast cancer risk

PURPOSE

Physical activity has been associated with reduced breast cancer risk, but studies of occupational activity have produced inconsistent results. The purpose of this study was to evaluate the relationship between occupational physical activity and breast cancer in a prospective study of women with a family history of breast cancer.

METHODS

We studied breast cancer risk in 47,649 Sister Study participants with an occupational history. Information on occupational activity and breast cancer risk factors was collected during baseline interviews (2004-2009). Physical activity at each job was self-reported and categorized as mostly sitting, sitting and standing equally, mostly standing, and active. Multivariable Cox proportional hazards regression was used to evaluate associations between lifetime occupational activity and incident breast cancer, after adjusting for established risk factors and recreational activity.

RESULTS

During follow-up, a total of 1,798 breast cancer diagnoses were reported. Compared with women who did not spend any time in active jobs, women who spent a high proportion (≥75%) of their working years in active jobs had a reduced risk of breast cancer (HR 0.72; 95% CI 0.52-0.98). Associations were strongest among overweight (HR 0.64; 95% CI 0.42-0.98) and postmenopausal (HR 0.67; 95% CI 0.45-0.98) women.

CONCLUSIONS

Occupational activity was associated with a reduced risk of breast cancer. Occupational activity is a domain of physical activity that should be further examined in studies of postmenopausal breast cancer risk. Additional research is necessary to better understand the mechanisms underlying the relationships between occupational activity, body size, and breast cancer.

Reduced risk of breast cancer associated with recreational physical activity varies by HER2 status

Convincing epidemiologic evidence indicates that physical activity is inversely associated with breast cancer risk. Whether this association varies by the tumor protein expression status of the estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), or p53 is unclear. We evaluated the effects of recreational physical activity on risk of invasive breast cancer classified by the four biomarkers, fitting multivariable unconditional logistic regression models to data from 1195 case and 2012 control participants in the population-based Women’s Contraceptive and Reproductive Experiences Study. Self-reported recreational physical activity at different life periods was measured as average annual metabolic equivalents of energy expenditure [MET]-hours per week. Our biomarker-specific analyses showed that lifetime recreational physical activity was negatively associated with the risks of ER-positive (ER+) and of HER2-negative (HER2−) subtypes (both P_trend ≤ 0.04), but not with other subtypes (all P_trend > 0.10). Analyses using combinations of biomarkers indicated that risk of invasive breast cancer varied only by HER2 status. Risk of HER2–breast cancer decreased with increasing number of MET-hours of recreational physical activity in each specific life period examined, although some trend tests were only marginally statistically significant (all P_trend ≤ 0.06). The test for homogeneity of trends (HER2– vs. HER2+ ) reached statistical significance only when evaluating physical activity during the first 10 years after menarche (P_homogeneity = 0.03). Our data suggest that physical activity reduces risk of invasive breast cancers that lack HER2 overexpression, increasing our understanding of the biological mechanisms by which physical activity acts.

Adherence to cancer prevention guidelines in 18 African countries

BACKGROUND

Cancer rates in Africa are projected to double by 2030 due to aging and increased exposure to cancer risk factors, including modifiable risk factors. We assessed adherence to 5 modifiable cancer risk factors across 18 African countries.

METHODS

Data on adults 18 years and older were obtained from the 2002-2004 World Health Survey. Adherence to current World Cancer Research Fund guidelines on smoking, alcohol, body weight, physical activity, and nutrition was assessed. Adherence scores ranged from 0 (no guideline met) to 5 (all guidelines met). Determinants of adherence were assessed using multivariable linear regression adjusted for individual and country level characteristics.

RESULTS

Across all countries, adherence to the guidelines among adults was high for smoking (72%-99%) and alcohol (85%-100%), but low for body weight (1.8%-78%), physical activity (3.4%-84%) and nutrition (1.4%-61%). Overall adherence score ranged from 2.32 in Mali to 3.72 in Comoros. In multivariable models, residing in low versus high SES households was associated with reduced adherence by 0.24 and 0.21 points for men and women respectively after adjusting for age, gender, education, and marital status (p<0.001). Every % increase in GDP spent on health was associated with increased adherence by 0.03 in men and 0.09 in women (p<0.001).

CONCLUSIONS

The wide variation in adherence to cancer prevention guidelines observed across countries and between population sub-groups suggests the need for targeted public health efforts to improve behaviors related to body weight, physical activity and nutrition.