Recreational physical activity and breast cancer risk by menopausal status and tumor hormone receptor status: results from the Nurses' Health Studies

PURPOSE

Physical activity is associated with lower breast cancer risk, especially in postmenopausal women. Associations in premenopausal women are less well established.

METHODS

We evaluated recreational physical activity and breast cancer risk in the Nurses' Health Study (NHS) and NHSII (187,278 women; n = 12,785 breast cancers; follow-up: NHS = 1986-2016, NHSII = 1989-2017) by menopausal status and estrogen (ER) and progesterone (PR) receptor status. Physical activity was evaluated as updated cumulative average of metabolic equivalent of task (MET)-h/week. Cox proportional hazards models were used to estimate multivariable hazard ratios (HR) and 95% confidence intervals (CI).

RESULTS

Recreational physical activity was inversely associated with breast cancer risk in pre- and postmenopausal women. Higher activity levels were associated with lower risk of ER+/PR + breast cancer in both pre- and postmenopausal women (e.g., total recreational activity, ≥ 27 vs < 3 MET-h/week, premenopausal HR = 0.83, 95%CI = (0.70-0.99), postmenopausal HR = 0.86 (0.78-0.95); pheterogeneity = 0.97). Results were attenuated with adjustment for current body mass index (BMI) among postmenopausal, but not premenopausal, women (e.g., ≥ 27 vs < 3 MET-h/week, premenopausal HR = 0.83 (0.69-0.98); postmenopausal HR = 0.95 (0.85-1.05); pheterogeneity = 0.99). In analyses of moderate-vigorous activity and breast cancer risk, no heterogeneity by menopausal status was observed (phet ≥ 0.53; e.g., ≥ 27 vs < 3 MET-h/week, ER+/PR+, premenopausal HR = 0.88 (0.69-1.11); postmenopausal HR = 0.71 (0.58-0.88). No associations were observed for ER-/PR- disease.

CONCLUSIONS

Recreational physical activity was associated with lower breast cancer risk in both pre- and postmenopausal women, supporting recreational physical activity as an accessible, modifiable exposure associated with reduced breast cancer risk regardless of menopausal status.

International Pooled Analysis of Leisure-Time Physical Activity and Premenopausal Breast Cancer in Women From 19 Cohorts

PURPOSE

There is strong evidence that leisure-time physical activity is protective against postmenopausal breast cancer risk but the association with premenopausal breast cancer is less clear. The purpose of this study was to examine the association of physical activity with the risk of developing premenopausal breast cancer.

METHODS

We pooled individual-level data on self-reported leisure-time physical activity across 19 cohort studies comprising 547,601 premenopausal women, with 10,231 incident cases of breast cancer. Multivariable Cox regression was used to estimate hazard ratios (HRs) and 95% CIs for associations of leisure-time physical activity with breast cancer incidence. HRs for high versus low levels of activity were based on a comparison of risk at the 90th versus 10th percentiles of activity. We assessed the linearity of the relationship and examined subtype-specific associations and effect modification across strata of breast cancer risk factors, including adiposity.

RESULTS

Over a median 11.5 years of follow-up (IQR, 8.0-16.1 years), high versus low levels of leisure-time physical activity were associated with a 6% (HR, 0.94 [95% CI, 0.89 to 0.99]) and a 10% (HR, 0.90 [95% CI, 0.85 to 0.95]) reduction in breast cancer risk, before and after adjustment for BMI, respectively. Tests of nonlinearity suggested an approximately linear relationship (Pnonlinearity = .94). The inverse association was particularly strong for human epidermal growth factor receptor 2-enriched breast cancer (HR, 0.57 [95% CI, 0.39 to 0.84]; Phet = .07). Associations did not vary significantly across strata of breast cancer risk factors, including subgroups of adiposity.

CONCLUSION

This large, pooled analysis of cohort studies adds to evidence that engagement in higher levels of leisure-time physical activity may lead to reduced premenopausal breast cancer risk.

Non-occupational physical activity and risk of cardiovascular disease, cancer and mortality outcomes: a dose-response meta-analysis of large prospective studies

OBJECTIVE

To estimate the dose-response associations between non-occupational physical activity and several chronic disease and mortality outcomes in the general adult population.

DESIGN

Systematic review and cohort-level dose-response meta-analysis.

DATA SOURCES

PubMed, Scopus, Web of Science and reference lists of published studies.

ELIGIBILITY CRITERIA

Prospective cohort studies with (1) general population samples >10 000 adults, (2) ≥3 physical activity categories, and (3) risk measures and CIs for all-cause mortality or incident total cardiovascular disease, coronary heart disease, stroke, heart failure, total cancer and site-specific cancers (head and neck, myeloid leukaemia, myeloma, gastric cardia, lung, liver, endometrium, colon, breast, bladder, rectum, oesophagus, prostate, kidney).

RESULTS

196 articles were included, covering 94 cohorts with >30 million participants. The evidence base was largest for all-cause mortality (50 separate results; 163 415 543 person-years, 811 616 events), and incidence of cardiovascular disease (37 results; 28 884 209 person-years, 74 757 events) and cancer (31 results; 35 500 867 person-years, 185 870 events). In general, higher activity levels were associated with lower risk of all outcomes. Differences in risk were greater between 0 and 8.75 marginal metabolic equivalent of task-hours per week (mMET-hours/week) (equivalent to the recommended 150 min/week of moderate-to-vigorous aerobic physical activity), with smaller marginal differences in risk above this level to 17.5 mMET-hours/week, beyond which additional differences were small and uncertain. Associations were stronger for all-cause (relative risk (RR) at 8.75 mMET-hours/week: 0.69, 95% CI 0.65 to 0.73) and cardiovascular disease (RR at 8.75 mMET-hours/week: 0.71, 95% CI 0.66 to 0.77) mortality than for cancer mortality (RR at 8.75 mMET-hours/week: 0.85, 95% CI 0.81 to 0.89). If all insufficiently active individuals had achieved 8.75 mMET-hours/week, 15.7% (95% CI 13.1 to 18.2) of all premature deaths would have been averted.

CONCLUSIONS

Inverse non-linear dose-response associations suggest substantial protection against a range of chronic disease outcomes from small increases in non-occupational physical activity in inactive adults. PROSPERO registration number CRD42018095481.

Physical activity from menarche-to-first pregnancy and risk of breast cancer: the California teachers study

PURPOSE

A longer menarche-to-first pregnancy window of susceptibility (WOS) is associated with increased breast cancer risk. Whether physical activity, an established preventive risk factor, during the menarche-to-first pregnancy WOS offsets breast cancer risk overall or for specific molecular subtypes is unclear.

METHODS

We examined the prospective association between physical activity during the menarche-to-first pregnancy WOS and breast cancer risk in the California Teachers Study (N = 78,940). Recreational physical activity at multiple timepoints were recalled at cohort entry, and converted to metabolic equivalent of task hours per week (MET-hrs/wk). We used multivariable Cox proportional hazards models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

We observed 5,157 invasive breast cancer cases over 21.6 years of follow-up. Longer menarche-to-first pregnancy WOS (≥ 20 vs. < 15 years) was associated with higher breast cancer risk (HR = 1.23, 95% CI = 1.13-1.34). Women with higher physical activity level during menarche-to-first pregnancy had lower risk of invasive breast cancer (≥ 40 vs. < 9 MET-hrs/wk: HR = 0.89, 95% CI = 0.83-0.97) and triple-negative subtype (≥ 40 vs. < 9 MET-hrs/wk: HR = 0.53, 95% CI = 0.32-0.87). No association was observed for luminal A-like and luminal B-like subtypes. Higher physical activity level was associated with lower breast cancer risk among women with moderate (15-19 years) menarche-to-first pregnancy intervals (≥ 40 vs. < 9 MET-hrs/wk: HR = 0.80, 95% CI = 0.69-0.92), but not with short (< 15 years) or long (≥ 20 years) intervals.

CONCLUSION

Physical activity during a WOS was associated with lower breast cancer risk in our cohort. Understanding timing of physical activity throughout the life course in relationship with breast cancer risk maybe important for cancer prevention strategies.

Leisure-time physical activity is associated with reduced risks of breast cancer and triple negative breast cancer in Nigerian women

BACKGROUND

Leisure-time physical activity(LTPA) is associated with a reduced risk of breast cancer, but this has less been investigated by cancer subtypes in Africans living in Sub-Saharan Africa(SSA). We examined the associations between LTPA and breast cancer including its subtypes in Nigerian women and explored the effect modification of body size on such associations.

METHODS

The sample included 508 newly diagnosed primary invasive breast cancer cases and 892 controls from the Nigerian Integrative Epidemiology of Breast Cancer(NIBBLE) Study. Immunohistochemical(IHC) analysis was available for 294 cases. Total metabolic equivalents(METs) per hour/week of LTPA were calculated and divided by quartiles(Q1 <3.75, Q2:3.75-6.69, Q3:6.70-14.74, Q4:14.75 ≤). We applied logistic regressions to estimate the adjusted Odds Ratios(ORs) between LTPA and breast cancer and by its molecular subtypes and whether age-adjusted associations are modified by BMI.

RESULTS

The mean age(Mean±SD) of cases vs. controls(45.5 ± 11.1vs.40.1 ± 9.0) was higher, and the mean total METs hour/week was higher in controls vs. cases(11.9 ± 14.9vs.8.3 ± 11.1,p-value<0.001). Overall, 43.2%(N = 127/294) were classified as HRP, and 41.8%(N = 123/294) as TNBC. Women in the higher LTPA quartiles(Q3-Q4) vs. Q1 had lower odds of having breast cancer(OR_Q4vs.Q1=0.51,95%CI:0.35-0.74) and TNBC(OR_Q4vs.Q1=0.51, 95%CI:0.27-0.96), but not HRP(OR_Q4vs.Q1=0.61,95%CI:0.34-1.09) after adjusting for age, age at first menarche, body size, breastfeeding, menopausal, parity, contraceptives, demographics, alcohol, smoking, and physical activity at home and work. Lastly, LTPA and its age-adjusted association with breast cancer was more pronounced in women with BMI< 30 vs. BMI 30 + .

CONCLUSIONS

LTPA may reduce the risk of breast cancer, especially TNBC, which is the more aggressive and prevalent molecular subtype of breast cancer in SSA.

Diet, Obesity, and Sedentary Lifestyle as Risk Factor of Breast Cancer among Women at Yogyakarta Province in Indonesia

BACKGROUND: Breast cancer prevalence remains high worldwide, including in Indonesia. Studies examining relationship between obesity, dietary habit, sedentary lifestyle, and breast cancer development are largely inconclusive. AIM: This study aimed to determine relationship between obesity, dietary habit, sedentary lifestyle, and breast cancer risk among women at Yogyakarta Province in Indonesia. METHODS: This was a cross-sectional study on 135 women selected purposively during March–May 2019. Binary logistic regression models were employed in the analysis with 0.05 considered significant. RESULTS: Among study subjects, 54.07% and 40% were, respectively, ≥40 years old and smokers. About 53.33% consumed preserved food 3–6 times/week, and 49% and 50.37% consumed sweet food and beverage >1 time/ day, respectively. High body mass index (BMI) and physical inactivity were associated with 93% and 85% breast cancer risk reductions (adjusted odds ratio [AOR]: 0.07, 95% confidence interval [CI]: 0.01–0.45, p < 0.01 and AOR: 0.15, 95% CI: 0.05–0.47, p < 0.001). Smoking showed no significant relationship. A waist circumference (WC) of ≤80 was linked to 78% breast cancer risk reduction. Sweet food, sweet beverage, and energy drink consumption of >1 time/day led to 96%, 36%, and 84% reductions of invasive breast cancer risks. Meanwhile, consumption of preserved food 3–6 times/weeks and soft drinks >1 time/day correlated with an increased risk of breast cancer. CONCLUSION: High BMI, physical inactivity, and lower WC were associated with the lower breast cancer risk, while preserved food and soft drink consumption significantly increase the risk. Although sedentary lifestyle seems to have a small protective effect, healthy lifestyle should be encouraged and effective strategies are required to encourage women to adopt healthy lifestyle.

Prevalent diabetes and risk of total, colorectal, prostate and breast cancers in an ageing population: meta-analysis of individual participant data from cohorts of the CHANCES consortium

BACKGROUND

We investigated whether associations between prevalent diabetes and cancer risk are pertinent to older adults and whether associations differ across subgroups of age, body weight status or levels of physical activity.

METHODS

We harmonised data from seven prospective cohort studies of older individuals in Europe and the United States participating in the CHANCES consortium. Cox proportional hazard regression was used to estimate the associations of prevalent diabetes with cancer risk (all cancers combined, and for colorectum, prostate and breast). We calculated summary risk estimates across cohorts using pooled analysis and random-effects meta-analysis.

RESULTS

A total of 667,916 individuals were included with an overall median (P25-P75) age at recruitment of 62.3 (57-67) years. During a median follow-up time of 10.5 years, 114,404 total cancer cases were ascertained. Diabetes was not associated with the risk of all cancers combined (hazard ratio (HR) = 0.94; 95% confidence interval (CI): 0.86-1.04; I2 = 63.3%). Diabetes was positively associated with colorectal cancer risk in men (HR = 1.17; 95% CI: 1.08-1.26; I2 = 0%) and a similar HR in women (1.13; 95% CI: 0.82-1.56; I2 = 46%), but with a confidence interval including the null. Diabetes was inversely associated with prostate cancer risk (HR = 0.81; 95% CI: 0.77-0.85; I2 = 0%), but not with postmenopausal breast cancer (HR = 0.96; 95% CI: 0.89-1.03; I2 = 0%). In exploratory subgroup analyses, diabetes was inversely associated with prostate cancer risk only in men with overweight or obesity.

CONCLUSIONS

Prevalent diabetes was positively associated with colorectal cancer risk and inversely associated with prostate cancer risk in older Europeans and Americans.

Obese Adipose Tissue as a Driver of Breast Cancer Growth and Development: Update and Emerging Evidence

Obesity is an established risk factor for breast cancer growth and progression. A number of advances have been made in recent years revealing new insights into this link. Early events in breast cancer development involve the neoplastic transformation of breast epithelial cells to cancer cells. In obesity, breast adipose tissue undergoes significant hormonal and inflammatory changes that create a mitogenic microenvironment. Many factors that are produced in obesity have also been shown to promote tumorigenesis. Given that breast epithelial cells are surrounded by adipose tissue, the crosstalk between the adipose compartment and breast epithelial cells is hypothesized to be a significant player in the initiation and progression of breast cancer in individuals with excess adiposity. The present review examines this crosstalk with a focus on obese breast adipose-derived estrogen, inflammatory mediators and adipokines, and how they are mechanistically linked to breast cancer risk and growth through stimulation of oxidative stress, DNA damage, and pro-oncogenic transcriptional programs. Pharmacological and lifestyle strategies targeting these factors and their downstream effects are evaluated for feasibility and efficacy in decreasing the risk of obesity-induced breast epithelial cell transformation and consequently, breast cancer development.

Adrenergic Signaling in Immunotherapy of Cancer: Friend or Foe?

Simple Summary

Exercise is associated with many aspects of a healthy lifestyle. Among these, exercise leads to the secretion of adrenaline and noradrenaline, which mobilize cells of the immune system, a process which is suggested to possess therapeutic value in cancer therapy, alone or in combination with immunotherapy. Strikingly, administration of β-blockers—which block the effect of adrenaline/noradrenaline—are also suggested to be useful in cancer therapy alone or in combination with immunotherapy. Herein we discuss the question of whether exercise and the administration of β-blockers could potentially be useful in cancer therapy.

Abstract

The incidence of cancer is increasing worldwide, which is to a large extent related to the population’s increasing lifespan. However, lifestyle changes in the Western world are causative as well. Exercise is intrinsically associated with what one could call a “healthy life”, and physical activity is associated with a lower risk of various types of cancer. Mouse models of exercise have shown therapeutic efficacy across numerous cancer models, at least in part due to the secretion of adrenaline, which mobilizes cells of the immune system, i.e., cytotoxic T and natural killer (NK) cells, through signaling of the β-2 adrenergic receptor (β2AR). Clinical trials aiming to investigate the clinical value of exercise are ongoing. Strikingly, however, the use of β-blockers—antagonists of the very same signaling pathway—also shows signs of clinical potential in cancer therapy. Cancer cells also express β-adrenergic receptors (βARs) and signaling of the receptor is oncogenic. Moreover, there are data to suggest that β2AR signaling in T cells renders the cell functionally suppressed. In this paper, we discuss these seemingly opposing mechanisms of cancer therapy—exercise, which leads to increased β2AR signaling, and β-blocker treatment, which antagonizes that same signaling—and suggest potential mechanisms and possibilities for their combination.

Sedentary work and breast cancer risk: A systematic review and meta-analysis

OBJECTIVES

This systematic review and meta-analysis aimed to assess sedentary work's contribution to breast cancer risk quantitatively using thorough research articles.

METHODS

We performed a meta-analysis using a registered protocol in PROSPERO (registration number: CRD42020204629). Literature from PubMed, Embase, and Cochrane involving sedentary work and breast cancer risk was reviewed. We calculated the overall pooled risk ratios (RRs) and 95% CI with a random-effect model from the included studies. Furthermore, we performed stratified analyses by characteristics of studies.

RESULTS

Thirty-one studies (13 cohort studies and 18 case-control studies) were included in the analysis. The overall effect of the pooled analysis was an RR of 1.16 (95% CI 1.08-1.23). The results were 1.20 (95% CI 1.10-1.30) and 1.12 (95% CI 1.02-1.23) for cohort and case-control studies. The effect of sedentary work did not seem to be consistently attenuated by controlling body mass index, menopausal status, or experience of hormone replacement therapy.

CONCLUSION

The results from this meta-analysis suggest that sedentary behavior within the occupational domain was associated with a 15.5% increased risk of breast cancer. It is essential to reduce the sedentary time spent at work and to secure time for leisure-time physical activity among sedentary workers as a primary preventive measure.

Association of job category and occupational activity with breast cancer incidence in Japanese female workers: the JACC study

BACKGROUND

Breast cancer represented the leading cause of cancer deaths among women in Japan. Although physical activity has been reported protective against breast cancer, scientific evidence is limited on the risk of breast cancer according to job category or occupational activity in Japanese. Our objective was to examine the association of job category and occupational activity with breast cancer incidence in Japanese female workers using the data from the Japan Collaborative Cohort (JACC) Study.

METHODS

A prospective cohort study involving 19,041 women aged 40-79 years who have reported their occupational data and followed-up from 1988 to 2009. All variables were assessed by a self-administered questionnaire. Cancer incidence data were obtained from 24 areas of the JACC study through cancer population data registration, or review of hospital records. The Cox proportional hazard models were operated to calculate the hazard ratios (HRs) and corresponding 95% confidence intervals (CIs).

RESULTS

There were 138 incident cases of breast cancer during 13.3 years median follow-up period. Office workers compared with manual workers were at a higher risk of breast cancer after adjusting for reproductive health factors and physical activity indicators; the multivariable HR (95% CI) was 1.65 (1.07-2.55). Also, women who had mainly a sitting position during work compared with those moving during work had the higher risk: the multivariable HR (95%CI) of 1.45 (1.01-2.12). The excess risk of breast cancer was observed for office workers when time spent in walking was < 30 min/ day; HR (95% CI) was 1.11 (1.01-1.23), and for women mainly at a sitting position during work when time spent in walking was 30-59 min or < 30 min/day; HRs (95% CIs) were 1.87 (1.07-3.27) and 1.74 (1.07-2.83), respectively.

CONCLUSION

The job category and occupational activity were associated with risk of breast cancer incidence. A high risk was observed in office workers and in women with a sitting position during work. These observed increased risks were evident in women with less daily walking activity.

Association of physical activity, body mass index and reproductive history with breast cancer by menopausal status in Iranian women

BACKGROUND

The incidence rate of breast cancer (BC) is increasing in low- and middle-income countries (LMICs), including Iran. We investigated the association between BC risk and physical activity (PA), body mass index (BMI), and reproductive history among Iranian women.

METHODS

We conducted a large hospital-based case-control study and compared 958 BC cases with 967 controls at the Cancer Institute of Iran during 2011-2016. We used multiple logistic regression models and adjusted for potential confounders to estimate odds ratios (ORs) and 95% confidence intervals (95%CIs) for the associations between BC and different risk factors, including low physical activity.

RESULTS

Women with high levels of physical activity had a lower risk of BC compared to those who were inactive (OR = 0.55, 95%CI: 0.41, 0.75). In premenopausal women, the association was observed only in normal-weight women (OR = 0.31, 95%CI: 0.13, 0.75), while it was limited to obese women in the postmenopausal group (OR = 0.29, 95%CI: 0.12, 0.66). We found a high risk of postmenopausal BC among overweight (OR = 1.69; 95%CI: 1.01, 2.81) and obese women (OR = 1.9; 95%CI: 1.14, 3.14) compared to women with a normal BMI. We observed an inverse association among postmenopausal women who had between three and five children (OR = 0.31, 95%CI 0.14, 0.64) and more than six children (OR = 0.21, 95%CI 0.12, 0.42) compared to nulliparous women.

CONCLUSIONS

Low levels of physical activity, low parity, and being overweight or obese were major risk factors for BC. For the first time, we report a strong association between physical activity and BC risk in Iranian women.

World Cancer Research Fund International: Continuous Update Project-systematic literature review and meta-analysis of observational cohort studies on physical activity, sedentary behavior, adiposity, and weight change and breast cancer risk

PURPOSE

The purpose of the present study was to systematically review the complex associations between energy balance-related factors and breast cancer risk, for which previous evidence has suggested different associations in the life course of women and by hormone receptor (HR) status of the tumor.

METHODS

Relevant publications on adulthood physical activity, sedentary behavior, body mass index (BMI), waist and hip circumferences, waist-to-hip ratio, and weight change and pre- and postmenopausal breast cancer risk were identified in PubMed up to 30 April 2017. Random-effects meta-analyses were conducted to summarize the relative risks across studies.

RESULTS

One hundred and twenty-six observational cohort studies comprising over 22,900 premenopausal and 103,000 postmenopausal breast cancer cases were meta-analyzed. Higher physical activity was inversely associated with both pre- and postmenopausal breast cancers, whereas increased sitting time was positively associated with postmenopausal breast cancer. Although higher early adult BMI (ages 18-30 years) was inversely associated with pre- and postmenopausal breast cancers, adult weight gain and greater body adiposity increased breast cancer risk in postmenopausal women, and the increased risk was evident for HR+ but not HR- breast cancers, and among never but not current users of postmenopausal hormones. The evidence was less consistent in premenopausal women. There were no associations with adult weight gain, inverse associations with adult BMI (study baseline) and hip circumference, and non-significant associations with waist circumference and waist-to-hip ratio that were reverted to positive associations on average in studies accounting for BMI. No significant associations were observed for HR-defined premenopausal breast cancers.

CONCLUSION

Better understanding on the impact of these factors on pre- and postmenopausal breast cancers and their subtypes along the life course is needed.

Avoidable cancers in the Nordic countries-the potential impact of increased physical activity on postmenopausal breast, colon and endometrial cancer

BACKGROUND

Physical activity has been shown to reduce the risk of colon, endometrial and postmenopausal breast cancer. The aim of this study was to quantify the proportion of the cancer burden in the Nordic countries linked to insufficient levels of leisure time physical activity and estimate the potential for cancer prevention for these three sites by increasing physical activity levels.

METHODS

Using the Prevent macrosimulation model, the number of cancer cases in the Nordic countries over a 30-year period (2016-2045) was modelled, under different scenarios of increasing physical activity levels in the population, and compared with the projected number of cases if constant physical activity prevailed. Physical activity (moderate and vigorous) was categorised according to metabolic equivalents (MET) hours in groups with sufficient physical activity (15+ MET-hours/week), low deficit (9 to <15 MET-hours/week), medium deficit (3 to <9 MET-hours/week) and high deficit (<3 MET-hours/week).

RESULTS

If no one had insufficient levels of physical activity, about 11,000 colon, endometrial and postmenopausal breast cancer cases could be avoided in the Nordic countries in a 30-year period, which is 1% of the expected cases for the three cancer types. With a 50% reduction in all deficit groups by 2025 or a 100% reduction in the group of high deficit, approximately 0.5% of the expected cases for the three cancer types could be avoided. The number and percentage of avoidable cases was highest for colon cancer.

CONCLUSION

11,000 cancer cases could be avoided in the Nordic countries in a 30-year period, if deficit in physical activity was eliminated.

Breast Cancer Screening: Why Can't Everyone Agree?

Screening mammography and evolving treatments have improved mortality over the last 25 years. However, breast cancer remains the second leading cause of cancer-related mortality for women in the United States. There are several contradictory recommendations regarding breast cancer screening. Familiarity with these recommendations will allow physicians to counsel their patients and ensure well-informed shared decision making.

Blood pressure and risk of breast cancer, overall and by subtypes: a prospective cohort study

OBJECTIVE

Blood pressure (BP) and breast cancer may share a common pathophysiologic pathway involving chronic inflammation, hormone synthesis and metabolism. Previous studies investigating the association between BP and breast cancer measured BP at a single time point and did not examine associations by breast cancer molecular subtypes.

METHODS

We used data from 22 833 female participants in the Melbourne Collaborative Cohort Study. BP was objectively measured at baseline (1990-1994) and a follow-up visit (2003-2007). Cox regression was used to estimate hazard ratios for baseline BP and temporal changes in BP in relation to risk of breast cancer, overall and by molecular subtypes.

RESULTS

We did not observe any associations between BP measured at baseline and breast cancer risk overall (per 5 mmHg SBP, hazard ratio = 1.00, 95% confidence interval: 0.99-1.02), nor by subtype (per 5 mmHg SBP: estrogen-receptor-negative: hazard ratio = 0.99, 0.96-1.03, progesterone-receptor-negative: hazard ratio = 1.01, 0.99-1.04, human epidermal growth factor receptor 2 negative: hazard ratio = 1.00, 0.98-1.01). Temporal changes in BP were not associated with risk of breast cancer (per 5 mmHg change in SBP, hazard ratio = 1.00, 0.97-1.03). Increased DBP over time was associated with higher risk of triple-negative breast cancer (P = 0.04), based on a small number of cases (N = 41).

CONCLUSION

Our study supports previous findings of no association between BP and breast cancer. Similar conclusions were reached when assessing BP over time and when examining specific tumor subtypes.

Breast cancer risk prediction: an update to the Rosner-Colditz breast cancer incidence model

PURPOSE

To update and expand the Rosner-Colditz breast cancer incidence model by evaluating the contributions of more recently identified risk factors as well as predicted percent mammographic density (MD) to breast cancer risk.

METHODS

Using data from the Nurses' Health Study (NHS) and NHSII, we added adolescent somatotype (9 unit scale), vegetable intake (servings/day), breastfeeding (months), physical activity (MET-h/week), and predicted percent MD to the Rosner-Colditz model to determine whether these variables improved model discrimination. We evaluated all invasive as well as ER+/PR+, ER+/PR-, and ER-/PR- breast cancer.

RESULTS

In the NHS/NHSII, we accrued over 5200 cases of invasive breast cancer over more than 20 years of follow-up with complete data on the risk factors. Adolescent somatotype and predicted percent MD significantly improved the original Rosner-Colditz model for all invasive breast cancer (change in age-adjusted AUC = 0.020, p < 0.001). The relative risk (RR) of invasive breast cancer for a 4-unit increase in adolescent somatotype was 0.62 (95% CI 0.56, 0.70), whereas the RR for a 20-unit increase in predicted percent MD was 1.32 (95% CI 1.28, 1.36). Adolescent somatotype and predicted percent MD also significantly improved the ER+/PR+model (change in age-adjusted AUC = 0.020, p < 0.001) as well as the ER+/PR- model (change in age-adjusted AUC = 0.012, p = 0.007). Adolescent somatotype, predicted percent MD, breastfeeding, and vegetable intake improved the ER-/PR- model (change in AUC = 0.031, p < 0.0001). The RR of ER-/PR- disease for 5 vegetable servings/day increase was 0.83 (95% CI 0.70, 0.99), while the RR for every 12 months of breastfeeding was 0.88 (95% CI 0.77, 1.01). Physical activity did not improve risk classification in any model.

CONCLUSION

Adolescent somatotype and predicted percent MD significantly improved breast cancer risk classification using the Rosner-Colditz model. Further, risk factors specific to ER- disease, such as breastfeeding and vegetable intake, may also help improve risk prediction of this aggressive subtype.

Adherence to diet, physical activity and body weight recommendations and breast cancer incidence in the Black Women's Health Study

Adherence to cancer prevention recommendations has been associated with lower incidence of breast cancer in previous studies, but evidence in African American women is limited. This project evaluated the association between adherence to the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) cancer prevention recommendations and breast cancer incidence among African American women. The Black Women's Health Study (analytic cohort = 49,103) is an ongoing prospective cohort study of African American women, ages 21-69 years at baseline (1995). Adherence scores for seven WCRF/AICR recommendations (adherent = 1, partial adherence = 0.5, non-adherence = 0) were calculated using questionnaire data and summed for overall (maximum = 7) and diet only (maximum = 5) scores. Associations between baseline and time-varying adherence scores and breast cancer incidence (N = 1,827 incident cases through 2011) were evaluated using proportional hazards regression. In this cohort, 8.5% adhered >4 recommendations. Adherence at baseline was not associated with breast cancer incidence. Higher overall time-varying adherence (per 0.5 point increase) was associated with lower breast cancer incidence (HR: 0.90, 95% CI: 0.84-0.96). Adherence to physical activity, sugar beverage and red and processed meat recommendations were also associated with reduced risk. Adherence to the WCRF/AICR recommendations was low and may be associated with lower breast cancer incidence in African American women.

Vigorous physical activity and risk of breast cancer in the African American breast cancer epidemiology and risk consortium

The relationship between physical activity and breast cancer risk has been extensively studied among women of European descent, with most studies reporting inverse associations. However, data on American women of African ancestry (AA) and by tumor subtypes are sparse. Thus, we examined associations of vigorous exercise and breast cancer risk overall, and by estrogen receptor (ER) status, in the African American Breast Cancer Epidemiology and Risk Consortium. We pooled data from four large studies on 2482 ER+ cases, 1374 ER- cases, and 16,959 controls. Multivariable logistic regression was used to compute odds ratios (OR) and 95 % confidence intervals (CI) for the risk of breast cancer overall, and polytomous logistic regression was used to model the risk of ER+ and ER- cancer. Recent vigorous exercise was associated with a statistically significant, modestly decreased risk for breast cancer overall (OR 0.88, 95 % CI 0.81-0.96) and for ER+ cancer (OR 0.88, 95 % CI 0.80-0.98), but not for ER- cancer (OR 0.93, 95 % CI 0.82-1.06). Overall, there was no strong evidence of effect modification by age, menopausal status, body mass index, and parity. However, our data were suggestive of modification by family history, such that an inverse association was present among women without a family history but not among those with a relative affected by breast cancer. Results from this large pooled analysis provide evidence that vigorous physical activity is associated with a modestly reduced risk of breast cancer in AA women, specifically ER+ cancer.

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.

Association of Leisure-Time Physical Activity With Risk of 26 Types of Cancer in 1.44 Million Adults

IMPORTANCE

Leisure-time physical activity has been associated with lower risk of heart-disease and all-cause mortality, but its association with risk of cancer is not well understood.

OBJECTIVE

To determine the association of leisure-time physical activity with incidence of common types of cancer and whether associations vary by body size and/or smoking.

DESIGN, SETTING, AND PARTICIPANTS

We pooled data from 12 prospective US and European cohorts with self-reported physical activity (baseline, 1987-2004). We used multivariable Cox regression to estimate hazard ratios (HRs) and 95% confidence intervals for associations of leisure-time physical activity with incidence of 26 types of cancer. Leisure-time physical activity levels were modeled as cohort-specific percentiles on a continuous basis and cohort-specific results were synthesized by random-effects meta-analysis. Hazard ratios for high vs low levels of activity are based on a comparison of risk at the 90th vs 10th percentiles of activity. The data analysis was performed from January 1, 2014, to June 1, 2015.

EXPOSURES

Leisure-time physical activity of a moderate to vigorous intensity.

MAIN OUTCOMES AND MEASURES

Incident cancer during follow-up.

RESULTS

A total of 1.44 million participants (median [range] age, 59 [19-98] years; 57% female) and 186 932 cancers were included. High vs low levels of leisure-time physical activity were associated with lower risks of 13 cancers: esophageal adenocarcinoma (HR, 0.58; 95% CI, 0.37-0.89), liver (HR, 0.73; 95% CI, 0.55-0.98), lung (HR, 0.74; 95% CI, 0.71-0.77), kidney (HR, 0.77; 95% CI, 0.70-0.85), gastric cardia (HR, 0.78; 95% CI, 0.64-0.95), endometrial (HR, 0.79; 95% CI, 0.68-0.92), myeloid leukemia (HR, 0.80; 95% CI, 0.70-0.92), myeloma (HR, 0.83; 95% CI, 0.72-0.95), colon (HR, 0.84; 95% CI, 0.77-0.91), head and neck (HR, 0.85; 95% CI, 0.78-0.93), rectal (HR, 0.87; 95% CI, 0.80-0.95), bladder (HR, 0.87; 95% CI, 0.82-0.92), and breast (HR, 0.90; 95% CI, 0.87-0.93). Body mass index adjustment modestly attenuated associations for several cancers, but 10 of 13 inverse associations remained statistically significant after this adjustment. Leisure-time physical activity was associated with higher risks of malignant melanoma (HR, 1.27; 95% CI, 1.16-1.40) and prostate cancer (HR, 1.05; 95% CI, 1.03-1.08). Associations were generally similar between overweight/obese and normal-weight individuals. Smoking status modified the association for lung cancer but not other smoking-related cancers.

CONCLUSIONS AND RELEVANCE

Leisure-time physical activity was associated with lower risks of many cancer types. Health care professionals counseling inactive adults should emphasize that most of these associations were evident regardless of body size or smoking history, supporting broad generalizability of findings.

Body mass index and risk of luminal, HER2-overexpressing, and triple negative breast cancer

Triple negative (TN, tumors that do not express estrogen receptor (ER), progesterone receptor (PR), or human epidermal growth factor receptor 2 (HER2)) and HER2-overexpressing (H2E, ER-/HER2+) tumors are two particularly aggressive subtypes of breast cancer. There is a lack of knowledge regarding the etiologies of these cancers and in particular how anthropometric factors are related to risk. We conducted a population-based case-case study consisting of 2659 women aged 20-69 years diagnosed with invasive breast cancer from 2004 to 2012. Four case groups defined based on joint ER/PR/HER2 status were included: TN, H2E, luminal A (ER+/HER2-), and luminal B (ER+/HER2+). Polytomous logistic regression was used to estimate odds ratios (ORs) and associated 95 % confidence intervals (CIs) where luminal A patients served as the reference group. Obese premenopausal women [body mass index (BMI) ≥30 kg/m(2)] had an 82 % (95 % CI 1.32-2.51) increased risk of TN breast cancer compared to women whose BMI <25 kg/m(2), and those in the highest weight quartile (quartiles were categorized based on the distribution among luminal A patients) had a 79 % (95 % CI 1.23-2.64) increased risk of TN disease compared to those in the lowest quartile. Among postmenopausal women obesity was associated with reduced risks of both TN (OR = 0.74, 95 % CI 0.54-1.00) and H2E (OR = 0.47, 95 % CI 0.32-0.69) cancers. Our results suggest obesity has divergent impacts on risk of aggressive subtypes of breast cancer in premenopausal versus postmenopausal women, which may contribute to the higher incidence rates of TN cancers observed among younger African American and Hispanic women.

Physical activity, hormone replacement therapy and breast cancer risk: A meta-analysis of prospective studies

BACKGROUND

Lower risk of breast cancer has been reported among physically active women, but the risk in women using hormone replacement therapy (HRT) appears to be higher. We quantified the association between physical activity and breast cancer, and we examined the influence that HRT use and other risk factors had on this association.

METHODS

After a systematic literature search, prospective studies were meta-analysed using random-effect models applied on highest versus lowest level of physical activity. Dose-response analyses were conducted with studies reporting physical activity either in hours per week or in hours of metabolic equivalent per week (MET-h/week).

RESULTS

The literature search identified 38 independent prospective studies published between 1987 and 2014 that included 116,304 breast cancer cases. Compared to the lowest level of physical activity, the highest level was associated with a summary relative risk (SRR) of 0.88 (95% confidence interval [CI] 0.85, 0.90) for all breast cancer, 0.89 (95% CI 0.83, 0.95) for ER+/PR+ breast cancer and 0.80 (95% CI 0.69, 0.92) for ER-/PR- breast cancer. Risk reductions were not influenced by the type of physical activity (occupational or non-occupational), adiposity, and menopausal status. Risk reductions increased with increasing amounts of physical activity without threshold effect. In six studies, the SRR was 0.78 (95% CI 0.70, 0.87) in women who never used HRT and 0.97 (95% CI 0.88, 1.07) in women who ever used HRT, without heterogeneity in results. Findings indicate that a physically inactive women engaging in at least 150 min per week of vigorous physical activity would reduce their lifetime risk of breast cancer by 9%, a reduction that might be two times greater in women who never used HRT.

CONCLUSION

Increasing physical activity is associated with meaningful reductions in the risk of breast cancer, but in women who ever used HRT, the preventative effect of physical activity seems to be cancelled out.

Leisure time physical activity and cancer risk: evaluation of the WHO's recommendation based on 126 high-quality epidemiological studies

BACKGROUND

The WHO has concluded that physical activity reduces the risk of numerous diseases. However, few systemic reviews have been performed to assess the role of leisure time physical activity (LTPA) in lowering the risk of cancer in a dose-dependent manner and furthermore the suitability of recommendation of physical activity by the WHO.

METHODS

A systematic review and meta-analysis was designed to estimate cancer risk by LTPA in binary comparison and in a dose-dependent manner. MEDLINE and Web of Science were searched up to 30 December 2014 without language restrictions. Reference lists were reviewed for potential articles.

RESULTS

A total of 126 studies were recruited into the meta-analysis. Overall, the total cancer risk was reduced by 10% in people who undertook the most LTPA as compared with those who did the least. Dose-response meta-analysis indicated that the current WHO recommendation (equal to an average of 10 metabolic equivalents of energy hours per week) induced a 7% (95% CI 5% to 9%) cancer reduction. Moreover, the protective role of LTPA against cancer becomes saturated at 20 metabolic equivalents of energy hours per week, with a relative risk of 0.91 (95% CI 0.88 to 0.93). Subanalyses results based on cancer types showed that LTPA only exhibited significant protection against breast cancer and colorectal cancer.

CONCLUSIONS

Our meta-analysis indicates that the current WHO recommendation of physical activity can result in a 7% reduction in cancer risk, which is mainly attributed to its protective role against breast cancer and colorectal cancer. Furthermore, two-fold of current recommendation level is considered to give its saturated protection against cancer.

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.

Household physical activity and cancer risk: a systematic review and dose-response meta-analysis of epidemiological studies

Controversial results of the association between household physical activity and cancer risk were reported among previous epidemiological studies. We conducted a meta-analysis to investigate the relationship of household physical activity and cancer risk quantitatively, especially in dose-response manner. PubMed, Embase, Web of science and the Cochrane Library were searched for cohort or case-control studies that examined the association between household physical activity and cancer risks. Random–effect models were conducted to estimate the summary relative risks (RRs), nonlinear or linear dose–response meta-analyses were performed to estimate the trend from the correlated log RR estimates across levels of household physical activity quantitatively. Totally, 30 studies including 41 comparisons met the inclusion criteria. Total cancer risks were reduced 16% among the people with highest household physical activity compared to those with lowest household physical activity (RR = 0.84, 95% CI = 0.76–0.93). The dose-response analyses indicated an inverse linear association between household physical activity and cancer risk. The relative risk was 0.98 (95% CI = 0.97–1.00) for per additional 10 MET-hours/week and it was 0.99 (95% CI = 0.98–0.99) for per 1 hour/week increase. These findings provide quantitative data supporting household physical activity is associated with decreased cancer risk in dose-response effect.

Lifestyle, nutrition and breast cancer: facts and presumptions for consideration

Breast cancer is the most common cancer in women worldwide, and the high incidence of this cancer coupled with improvements in initial treatments has led to an ever-increasing number of breast cancer survivors. Among the prospective epidemiological studies on diet and breast cancer incidence and recurrence, to date, there is no association that is strong, reproducible and statistically significant, with the exception of alcohol intake, overweight, and weight gain. Nevertheless, many beliefs about food and breast cancer persist in the absence of supporting scientific evidence.

After a comprehensive review regarding the role of lifestyle on breast cancer outcomes and a thorough study of the dissemination field including mass media, clinical institutions, and academic figures, we briefly reported the most common presumptions and also facts from the literature regarding lifestyle, nutrition, and breast cancer.

The randomised controlled trial is the best study-design that could provide direct evidence of a causal relationship; however, there are methodological difficulties in applying and maintaining a lifestyle intervention for a sufficient period; consequently, there is a lack of this type of study in the literature. Instead, it is possible to obtain indirect evidence from observational prospective studies. In this article, it becomes clear that for now the best advice for women’s health is to follow the World Cancer Research Fund/American Institute of Cancer Research (WCRF/AICR) recommendations on diet, nutrition, physical activity, and weight management for cancer prevention, because they are associated with a lower risk of developing most types of cancer, including breast cancer. Despite current awareness of the role of nutrition in cancer outcomes, there is inadequate translation from research findings into clinical practice. We suggest the establishment of a multidisciplinary research consortium to demonstrate the real power of lifestyle interventions.

Adult body size and physical activity in relation to risk of breast cancer according to tumor androgen receptor status

BACKGROUND

Obesity and physical activity have been hypothesized to affect breast cancer risk partly via the androgen signaling pathway. We conducted the first study to evaluate these associations by tumor androgen receptor (AR) status.

METHODS

Height, weight, and physical activity were assessed using questionnaires in the Nurses' Health Study. AR, estrogen receptor (ER), and progesterone receptor (PR) status were determined using immunohistochemistry on tumor tissue and medical/pathology reports.

RESULTS

A total of 1,701 AR(+) and 497 AR(-) cases were documented during 26 years of follow-up of 103,577 women. After adjusting for ER/PR status and other risk factors, the relative risks (RR) and 95% confidence intervals (95% CI) for every 5 kg/m(2) increase in body mass index (BMI) were 1.07 (1.01-1.13) for AR(+) and 1.16 (1.05-1.29) for AR(-) tumors (P-heterogeneity = 0.17). The RRs (95% CIs) per 5 hours of brisk walking/week were 0.87 (0.73-1.04) for AR(+) and 0.67 (0.45-0.99) for AR(-) tumors (P-heterogeneity = 0.22). Further, BMI, but not physical activity, associations differed significantly across ER/PR/AR subtypes (P-heterogeneity = 0.04 and 0.63, respectively). The RRs (95% CIs) for 5 kg/m(2) increase in BMI were 1.23 (1.04-1.45) for ER(+)PR(+)AR(-), 1.19 (1.01-1.39) for ER(-)PR(-)AR(-), 1.15 (1.08-1.23) for ER(+)PR(+)AR(+), and 0.88 (0.75-1.03) for ER(+)PR(-)AR(+) tumors.

CONCLUSIONS

Higher BMI was associated with an increased risk of both AR(+) and AR(-) breast tumors in postmenopausal women, whereas physical activity, including brisk walking, was associated with a reduced risk of both subtypes. In addition, a significant positive association was observed between higher BMI and ER(-)PR(-)AR(-) tumors.

IMPACT

The similar associations observed by AR status suggest that mechanisms other than androgen signaling underlie these two breast cancer risk factors.

Energy-Related Indicators and Breast Cancer Risk among White and Black Women

Energy-related indicators, including physical activity, energy intake, body mass index (BMI) and adult weight change, have been linked to breast cancer risk. Very few studies of these associations have been conducted among black women, therefore we used the Nashville Breast Health Study (NBHS) to determine whether similar effects were seen in black and white women. The NBHS is a population-based case-control study of breast cancer among women age 25 to 75 years conducted between 2001 and 2010 in and around the Nashville Metropolitan area. Telephone interviews and self-administered food frequency questionnaires were completed with 2,614 incident breast cancer cases ascertained through hospitals and the statewide cancer registry, and 2,306 controls selected using random digit dialing. Among premenopausal white and black women, there was little effect of adult exercise or other energy-related indicators on breast cancer risk, regardless of tumor estrogen receptor (ER) status. The beneficial effect of adult exercise on postmenopausal breast cancer appeared to be comparable between white and black women (highest tertile relative to none - white odds ratio [OR] 0.8, 95% confidence interval [CI] 0.6-1.0, p for trend=0.05; black OR 0.7, 95% CI 0.4-1.1, p for trend=0.07); however, among black women the reduction was limited to those with ER-positive disease. White and black women should be encouraged to engage in more physical activity to reduce their risk of postmenopausal 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.

Vitamin D intake, blood 25(OH)D levels, and breast cancer risk or mortality: a meta-analysis

Background:

Experimental studies suggest potential anti-carcinogenic properties of vitamin D against breast cancer risk, but the epidemiological evidence to date is inconsistent.

Methods:

We searched MEDLINE and EMBASE databases along with a hand search for eligible studies to examine the association between vitamin D status (based on diet and blood 25-hydroxyvitamin D (25(OH)D)) and breast cancer risk or mortality in a meta-analysis. A random-effect model was used to calculate a pooled adjusted relative risk (RR).

Results:

A total of 30 prospective studies (nested case-control or cohort) were included for breast cancer incidence (n=24 studies; 31 867 cases) or mortality (n=6 studies; 870 deaths) among 6092 breast cancer patients. The pooled RRs of breast cancer incidence for the highest vs the lowest vitamin D intake and blood 25(OH)D levels were 0.95 (95% CI: 0.88–1.01) and 0.92 (95% CI: 0.83–1.02), respectively. Among breast cancer patients, high blood 25(OH)D levels were significantly associated with lower breast cancer mortality (pooled RR=0.58, 95% CI: 0.40–0.85) and overall mortality (pooled RR=0.61, 95% CI: 0.48–0.79). There was no evidence of heterogeneity and publication bias.

Conclusions:

Our findings suggest that high vitamin D status is weakly associated with low breast cancer risk but strongly associated with better breast cancer survival.

Physical activity and the risk of postmenopausal breast cancer - the Norwegian Women and Cancer Study

Background

The relationship between physical activity (PA) throughout life and the risk of postmenopausal breast cancer overall and by estrogen receptor (ER) and progesterone receptor (PR) status, has been reported, but without consistent results. The present study aimed to investigate PA from young age to adulthood in participants of the Norwegian Women and Cancer (NOWAC) Study, in order to determine whether changes in PA level affect the risk of postmenopausal breast cancer.

Methods

1767 invasive breast cancer cases were identified among 80,202 postmenopausal participants of the NOWAC Study during 8.2 years of median follow-up. PA levels at age 14 years, 30 years and at cohort enrollment were obtained via a self-administered questionnaire. Multivariate Cox proportional hazard regression models were used to estimate relative risks and 95% confidence intervals of the risk of postmenopausal breast cancer overall and by ER/PR status.

Results

Risk of postmenopausal breast cancer overall and by ER/PR status was not associated with physical activity level at enrollment. Women with a low PA level at age 30 had an increased risk of ER+/PR + breast tumors (P for trend = 0.04) compared to women with a moderate physical activity level at age 30. Women with a low physical activity level at all three periods of life had a 20% significantly reduced risk of postmenopausal breast cancer, as well as a reduced risk of ER+/PR + and ER+/PR- breast tumors, compared with women who maintained a moderate physical activity level. However, when analyses were corrected for multiple tests, the result was no longer statistically significant. The findings were consistent over strata of age, body mass index and use of hormone replacement therapy.

Conclusions

The study results from this large Norwegian cohort do not support an association between physical activity at different periods of life and the risk of postmenopausal breast cancer.

The role of metabolic carcinogenesis in cancer causation and prevention: evidence from the European Prospective Investigation into Cancer and Nutrition

The theory that nutrition might be involved in the causation and prevention of cancer arose over 100 years ago from laboratory studies of the effect of diet on tumour growth. During the mid-20th century, the major focus of cancer epidemiology was on the role of tobacco and alcohol. It was not until the early 1980s, following a seminal report from Doll and Peto on cancer causes, that major research programmes on nutrition and cancer were instigated. The European Prospective Investigation into Cancer and Nutrition (EPIC) was established at IARC-WHO as a large prospective cohort study designed specifically to investigate the relationship of diet, nutritional factors, anthropometry and physical activity with cancer risk. Since the early 1990s, EPIC has made a major contribution to understanding the effect of these factors on population risk of cancer. This chapter summarises the development of the field of nutritional cancer epidemiology, and describes how the EPIC study was designed to investigate cancer and nutrition. Key findings from EPIC in the role of nutrition and metabolic factors and cancer are highlighted.