Lifetime physical activity and risk of breast cancer in pre-and post-menopausal women

Associations between transport modes and site-specific cancers: a systematic review and meta-analysis

BACKGROUND

Physical inactivity is a global public health problem. A practical solution would be to build physical activity into the daily routine by using active modes of transport. Choice of transport mode can influence cancer risk through their effects on levels of physical activity, sedentary time, and environmental pollution. This review synthesizes existing evidence on the associations of specific transport modes with risks of site-specific cancers.

METHODS

Relevant literature was searched in PubMed, Embase, and Scopus from 1914 to 17th February 2023. For cancer sites with effect measures available for a specific transport mode from two or more studies, random effects meta-analyses were performed to pool relative risks (RR) comparing the highest vs. lowest activity group as well as per 10 Metabolic Equivalent of Task (MET) hour increment in transport-related physical activity per week (∼150 min of walking or 90 min of cycling).

RESULTS

27 eligible studies (11 cohort, 15 case-control, and 1 case-cohort) were identified, which reported the associations of transport modes with 10 site-specific cancers. In the meta-analysis, 10 MET hour increment in transport-related physical activity per week was associated with a reduction in risk for endometrial cancer (RR: 0.91, 95% CI: 0.83-0.997), colorectal cancer (RR: 0.95, 95% CI: 0.91-0.99) and breast cancer (RR: 0.99, 95% CI: 0.89-0.996). The highest level of walking only or walking and cycling combined modes, compared to the lowest level, were significantly associated with a 12% and 30% reduced risk of breast and endometrial cancers respectively. Cycling, compared to motorized modes, was associated with a lower risk of overall cancer incidence and mortality.

CONCLUSION

Active transport appears to reduce cancer risk, but evidence for cancer sites other than colorectum, breast, and endometrium is currently limited.

What Is Known about Breast Cancer in Young Women?

Breast cancer (BC) is the second leading cause of cancer-related death in women under the age of 40 years worldwide. In addition, the incidence of breast cancer in young women (BCYW) has been rising. Young women are not the focus of screening programs and BC in younger women tends to be diagnosed in more advanced stages. Such patients have worse clinical outcomes and treatment complications compared to older patients. BCYW has been associated with distinct tumour biology that confers a worse prognosis, including poor tumour differentiation, increased Ki-67 expression, and more hormone-receptor negative tumours compared to women >50 years of age. Pathogenic variants in cancer predisposition genes such as BRCA1/2 are more common in early-onset BC compared to late-onset BC. Despite all these differences, BCYW remains poorly understood with a gap in research regarding the risk factors, diagnosis, prognosis, and treatment. Age-specific clinical characteristics or outcomes data for young women are lacking, and most of the standard treatments used in this subpopulation currently are derived from older patients. More age-specific clinical data and treatment options are required. In this review, we discuss the epidemiology, clinicopathologic characteristics, outcomes, treatments, and special considerations of breast cancer in young women. We also underline future directions and highlight areas that require more attention in future studies.

Breast cancer subtype and clinical characteristics in women from Peru

Introduction

Breast cancer is a heterogeneous disease, and the distribution of the different subtypes varies by race/ethnic category in the United States and by country. Established breast cancer-associated factors impact subtype-specific risk; however, these included limited or no representation of Latin American diversity. To address this gap in knowledge, we report a description of demographic, reproductive, and lifestyle breast cancer-associated factors by age at diagnosis and disease subtype for The Peruvian Genetics and Genomics of Breast Cancer (PEGEN-BC) study.

Methods

The PEGEN-BC study is a hospital-based breast cancer cohort that includes 1943 patients diagnosed at the Instituto Nacional de Enfermedades Neoplásicas in Lima, Peru. Demographic and reproductive information, as well as lifestyle exposures, were collected with a questionnaire. Clinical data, including tumor Hormone Receptor (HR) status and Human Epidermal Growth Factor Receptor 2 (HER2) status, were abstracted from electronic medical records. Differences in proportions and mean values were tested using Chi-squared and one-way ANOVA tests, respectively. Multinomial logistic regression models were used for multivariate association analyses.

Results

The distribution of subtypes was 52% HR+HER2-, 19% HR+HER2+, 16% HR-HER2-, and 13% HR-HER2+. Indigenous American (IA) genetic ancestry was higher, and height was lower among individuals with the HR-HER2+ subtype (80% IA vs. 76% overall, p=0.007; 152 cm vs. 153 cm overall, p=0.032, respectively). In multivariate models, IA ancestry was associated with HR-HER2+ subtype (OR=1.38,95%CI=1.06-1.79, p=0.017) and parous women showed increased risk for HR-HER2+ (OR=2.7,95%CI=1.5-4.8, p<0.001) and HR-HER2- tumors (OR=2.4,95%CI=1.5-4.0, p<0.001) compared to nulliparous women. Multiple patient and tumor characteristics differed by age at diagnosis (<50 vs. >=50), including ancestry, region of residence, family history, height, BMI, breastfeeding, parity, and stage at diagnosis (p<0.02 for all variables).

Discussion

The characteristics of the PEGEN-BC study participants do not suggest heterogeneity by tumor subtype except for IA genetic ancestry proportion, which has been previously reported. Differences by age at diagnosis were apparent and concordant with what is known about pre- and post-menopausal-specific disease risk factors. Additional studies in Peru should be developed to further understand the main contributors to the specific age of onset and molecular disease subtypes in this population and develop population-appropriate predictive models for prevention.

Effect of Post-diagnosis Physical Activity on Breast Cancer Recurrence: a Systematic Review and Meta-analysis

PURPOSE OF REVIEW

Breast cancer (BC) recurrence dramatically decreases 5-year survival, which causes a fear of BC recurrence among a majority of BC survivors. Evidence is currently inconsistent on whether post-diagnosis recreational physical activity (rPA) can prevent BC recurrence due to the small number of included studies, as well as methodological heterogeneity among the studies. This systematic review aimed to clarify the association between post-diagnosis rPA and the risk of BC recurrence, by conducting a meta-analysis while controlling for the categories of rPA across the existing studies.

RECENT FINDINGS

Prospective cohort studies were searched, and five studies were eligible for the meta-analysis. Of 10,094 patients with BC, 1561 had recurrence during the follow-up period ranging from 12 to 156 months. The meta-analysis revealed that patients whose post-diagnosis rPA was ≥ 7.5 metabolic equivalents (MET-h/week) had a lower BC risk than patients whose rPA was 0-3 MET-h/week (hazard ratio [HR], 0.65; 95% CI, 0.58-0.73, p < 0.00001, I² = 0%). The review indicated that a post-diagnosis rPA of ≥ 7.5 MET-h/week could reduce the risk of BC recurrence by 35%. Although it is necessary to investigate randomized controlled studies in the future, this result will strengthen strategies for the care and/or treatment of patients after BC and can motivate BC survivors to participate in rPA programs after BC diagnosis.

Physical exercise in menopause: a review of physiological changes

Menopause is characterised by several hormonal changes through which women undergo aging. These changes lead to psychological, somatic, urogenital and vasomotor symptoms that influence the quality of life of women. Studies have shown that physical exercise can benefit women in the pre- and postmenopausal stages. However, the physiological benefits of exercise during the menopausal period have been less explored, as well as which type of exercise is most recommended at this stage of life. Therefore, the present review aimed to investigate the physiological changes promoted by the practice of physical exercise during the menopause period. A search for scientific articles was performed in the PubMed database using the descriptors ‘menopause’ and ‘exercise’ and the ‘AND’ connector. The period selected for this study was from 2014 to 2018. After applying the inclusion and exclusion criteria, five articles were selected. As a result, studies suggest that physical exercise promotes hormones, body composition and positive cardiovascular changes, decreases menopausal symptoms and improves psychosocial health. In addition, it is associated with an improvement in the quality of life.

Associations between Pre-Diagnostic Physical Activity with Breast Cancer Characteristics and Survival

Physical activity (PA) is known to reduce breast cancer (BC) risk and improve patient prognosis. However, the association between pre-diagnostic PA and the aggressiveness of BC is unclear. We investigated the associations between PA, BC tumour characteristics, and survival. This retrospective observational study included 7688 BC patients from the Singapore Breast Cancer Cohort (2010−2016). PA information from the questionnaire included intensity (light/moderate/vigorous) and duration (<1 h/1−2 h/>2 h per week). A PA score (1−5) incorporating intensity and duration was calculated. Associations between PA score and tumour characteristics such as stage, histological grade, nodal and hormone receptor status were examined using multinomial regression. Moreover, 10-year overall survival was estimated using Cox regression analysis in 6572 patients after excluding patients with invalid survival data and stage IV disease. Breast tumours associated with higher PA score were more likely to be non-invasive (ORinvasive vs. non-invasive(reference) [95% CI]: 0.71 [0.58−0.87], p-trend = 0.001), of lower grade (ORpoorly vs. well differentiated(reference): 0.69 [0.52−0.93], p = 0.014), ER-positive (ORER-negative vs. ER-positive(reference): 0.94 [0.89−1.00], p-trend = 0.049), PR-positive (ORPR-negative vs. PR-positive(reference): 0.82 [0.67−0.99], p = 0.041), HER2-negative (ORHER2-negative vs. HER2-positive(reference): 1.29 [1.02−1.62], p-trend = 0.002), and less likely to be of HER2-overexpressed subtype (ORHER2-overexpressed vs. Luminal A(reference): 0.89 [0.81−0.98], p-trend = 0.018). These associations (odds ratios) were more pronounced among post-menopausal patients. A higher PA score did not improve survival. Higher levels of pre-diagnostic PA were associated with less aggressive tumours in BC patients. This illustrated another benefit of PA in addition to its known role in BC risk reduction.

Individual and additive-effect relationships of sleep problems and severe menopausal symptoms among women in menopausal transition

OBJECTIVE

Sleep problems and menopausal symptoms are both common complaints among midlife women. However, the associations of the quality and quantity of sleep problems with the severity of menopausal symptoms have not been well studied. Thus, this study aims to examine the relationships between individual sleep problems and the additive number of sleep problems with severe menopausal symptoms among women during the menopausal transition.

METHODS

Using the convenience sampling, a total of 848 middle-aged women in China were investigated from December 2017 to August 2018. All participants completed a questionnaire on sleep problems, Menopause Rating Scale, and the general information questionnaire. Based on the cutoff of the Menopause Rating Scale, participants were divided into the nonsevere menopausal symptom group and severe menopausal symptoms group. Propensity score matching was used to balance covariates between the two groups. Stepwise binary logistic regression and restricted cubic spline were applied to analyze the associations of individual and additive sleep problems with severe menopausal symptoms.

RESULTS

After propensity score matching, no significant difference was observed between the nonsevere menopausal symptoms group and severe menopausal symptoms group (Ps > 0.05). Logistic regression analysis showed that five sleep problems ("feeling too hot," "having pain," "restless legs syndrome," "taking medicine to help sleep," and "having trouble staying awake") were closely associated with severe menopausal symptoms. The restricted cubic spline curve showed an upward trend in odds ratios between the number of these five sleep problems and severe menopausal symptoms, and women were more than twice as likely to suffer severe menopausal symptoms when they experienced more than three of these individual sleep problems.

CONCLUSION

Both the individual and additive number of sleep problems exerted significant effects on severe menopausal symptoms. It might be useful for healthcare providers to set guidelines to support a healthy menopausal transition for midlife women.

Influence of physical activity at a young age and lifetime physical activity on the risks of 3 obesity-related cancers: systematic review and meta-analysis of observational studies

CONTEXT

Excess weight has been linked to increased risks of 13 types of cancers. Physical activity is a non-nutritional modifiable lifestyle factor that is not only crucial for weight control but is also known to regulate hormones and metabolic pathways that may contribute to carcinogenesis. There is solid evidence that being physically active during middle and late adulthood lowers the risks of 3 obesity-related cancers, namely breast cancer, colon cancer, and endometrial cancer. However, the associations between physical activity at a young age (childhood, adolescence, and young adulthood; age 5 to ≤30 yr) and lifetime physical activity and the risks of breast cancer, colon cancer, and endometrial cancer are less defined.

OBJECTIVE

The present systematic review and meta-analysis of observational studies was performed in accordance with the MOOSE guidelines to determine whether physical activity at a young age and lifetime physical activity may lower the risks of breast cancer, colon cancer, and endometrial cancer.

DATA SOURCES

The PubMed and Web of Science databases were searched for relevant observational studies published from inception to July 2018.

STUDY SELECTION

Observational studies (prospective cohort, case-cohort, nested case-control, historical cohort, and case-control) were considered relevant if they investigated the association between physical activity at a young age or lifetime physical activity and the risks of developing selected cancers.

DATA EXTRACTION

A random-effects meta-analysis was performed to generate the summary relative risk (RR) with 95%CI for the highest vs the lowest category of physical activity of any type.

RESULTS

Eighty publications were included in the present meta-analysis. Higher physical activity at a young age was associated with lower risks of breast cancer (RR 0.81, 95%CI 0.76, 0.87) and colon cancer (RR 0.67, 95%CI 0.50, 0.88). Similarly, lifetime physical activity was inversely associated with the risks of breast cancer (RR 0.79, 95%CI 0.72, 0.86) and colon cancer (RR 0.75, 95%CI 0.69, 0.82). For breast cancer, menopausal status did not appear to modify the observed inverse association. The benefit with respect to endometrial cancer risk reduction was only observed with higher lifetime physical activity (RR 0.77, 95%CI 0.67, 0.88), not with higher physical activity at a young age (RR 0.89, 95%CI 0.73, 1.07).

CONCLUSIONS

Being physically active over a lifetime, starting from early childhood, may lower the risks of developing breast cancer, colon cancer, and endometrial cancer.

Lifestyle and occupational factors associated with participation in breast mammography screening among Western Australian women

Objectives

Various lifestyle and occupational factors have been associated with an increased risk of breast cancer, but there is limited research investigating the relationship between these factors and participation in breast cancer screening. This study explores the associations between lifestyle and occupational factors and participation in breast mammography screening among women living in Western Australia.

Methods

This study involved 1705 women aged 40 and older who participated as controls in the Breast Cancer Environment and Employment Study conducted in Western Australia. Self-reported questionnaire data were collected on participation in mammography screening, demographic factors, and lifestyle and occupational variables (smoking, physical activity, alcohol consumption, body mass index, use of contraceptive pill and hormone replacement therapy, breastfeeding, occupation, and participation in shift work). Multivariate modified Poisson regression was used to identify variables associated with ever participation in breast mammography screening.

Results

Just over 88% of women reported having ever had a mammogram. Likelihood of having ever had a mammogram was higher among women who had ever used hormone replacement therapy (adjusted prevalence ratio (aPR) = 1.05, 95% CI 1.02–1.07). Women who worked in clerical occupations (aPR = 1.06, 95% CI 1.01–1.11) or home duties (aPR = 1.05, 95% CI 1.00–1.11) were also more likely to report having ever had a mammogram compared with those in professional or technical occupations.

Conclusions

Participation in mammography screening was found to differ by lifestyle and occupational factors. These results have important implications for public health strategies on improving screening participation.

High Bone Mineral Density of the Lumbar Spine Is Positively Associated with Breast Cancer

Objective

The objective of this study was to verify possible associations between bone mineral density (BMD) and breast cancer in recently diagnosed women in the Brazilian Mid-west region, considering the menopausal status of patients.

Methods

A case-control study was conducted with 142 cases of breast cancer and 234 controls matched by for age, body mass index (BMI), and menopausal status (pre- and postmenopause), performed in a university hospital in the Brazilian Mid-west. Lumbar spine (L1–L4), femoral neck, and total femur BMD were measured by the dual-energy X-ray absorptiometry (DXA) method. For association, a logistic regression analysis was used.

Results

Women in the highest lumbar spine BMD quartile presented had a higher chance of developing breast cancer (OR = 2.31; 1.02–5.25; p = 0.045), after adjusting for the confounding variables. Nonetheless, there were no statistically significant differences in the association between pre- and postmenopause in that quartile and breast cancer.

Conclusions

High lumbar spine BMD was positively associated with breast cancer in the total sample. In evaluating the BMD of the femoral neck and total femur, such an association was not observed.

Possible role of stress, coping strategies, and life style in the development of breast cancer

Objective The aim of the present study was to investigate the possibility of the effect of life long stressful events, along with coping method used, perception of social support, and life style on the development of breast cancer. Methods In this hospital-based case control study, the study group comprised 250 women with breast cancer who were followed by Florence Nightingale Breast Study Group. Control group included 250 women, who had similar sociodemographic characteristics to the study group. Data were collected with semi-structured interview form, Healthy Life Style Behavior Scale, Coping Strategy Indicator, and Stress Evaluation Form developed by us. Results In multivariate analysis, family history of cancer (OR: 1.55, 95% CI: 2.29-1.05), inadequate social support (OR: 1.83, 95% CI: 1.23-2.73), and loss of father during childhood (OR: 2.68, 95% CI: 5.52-1.30) and serious stressor within the last five years (OR: 4.72, 95% CI: 7.03-3.18) were found to be risk factors increasing the risk of breast cancer. When family history of cancer was excluded from the model, the presence of psychiatric disorder history (OR: 1.95, 95% CI: 3.26-1.17) and major life events (OR: 2.24, 95% CI: 4.07-1.24) were added to the model as risk factors. Conclusion The present study indicates that especially the stressful events experienced within the last five years plays an undeniable role in the risk of breast cancer. Social support may be as important in the period before the diagnosis as in the period after diagnosis.

Behavioral risk factors of breast cancer in Bangui of Central African Republic: A retrospective case-control study

Breast cancer is recognized as a major public health problem in developing countries; however, there is very little evidence of behavioral factors associated with breast cancer risk. This study was conducted to identify lifestyles as risk factors for breast cancer among Central African women. A case-control study was conducted with 174 cases confirmed histologically by the pathology unit of the National Laboratory and 348 age-matched controls. Data collection tools included a questionnaire with interviews and medical records of patients. Data were analyzed using SPSS software version 20. Odd ratio (OR) and 95% confidence intervals (95% CI) were obtained by unconditional logistic regression. In total, 522 women were studied with a mean age of 45.8 (SD = 13.4) years. By unconditional logistic regression model, women with breast cancer were more likely to have attained illiterate and elementary education level [11.23 (95% CI, 4.65-27.14) and 2.40 (95% CI, 1.15-4.99)], married [2.09 (95% CI, 1.18-3.71)], positive family history [2.31 (95% CI, 1.36-3.91)], radiation exposure [8.21 (95% CI, 5.04-13.38)], consumption charcuterie [10.82 (95% CI, 2.39-48.90)], fresh fish consumption [4.26 (95% CI, 1.56-11.65)], groundnut consumption [6.46 (95% CI, 2.57-16.27)], soybean consumption [16.74 (95% CI, 8.03-39.84)], alcohol [2.53 (95% CI, 1.39-4.60)], habit of keeping money in bras[3.57 (95% CI, 2.24-5.69)], overweight [5.36 (95% CI, 4.46-24.57)] and obesity [3.11(95% CI, 2.39-20.42)]. However, decreased risk of breast cancer was associated with being employed [0.32 (95% CI, 0.19-0.56)], urban residence [0.16 (95% CI, 0.07-0.37)], groundnut oil consumption [0.05 (95% CI, 0.02-0.14)], wine consumption [0.16 (95% CI, 0.09-0.26)], non habit of keeping cell phone in bras [0.56 (95% CI, 0.35-0.89)] and physical activity [0.71(95% CI, 0.14-0.84)]. The study showed that little or no education, marriage, positive family history of cancer, radiation exposure, charcuterie, fresh fish, groundnut, soybean, alcohol, habit of keeping money in bras, overweight and obesity were associated with breast cancer risk among Central African women living in Bangui. Women living in Bangui should be more cautious on the behavioral risk associated with breast cancer.

Reallocating Time to Sleep, Sedentary Time, or Physical Activity: Associations with Waist Circumference and Body Mass Index in Breast Cancer Survivors

BACKGROUND

Moderate-to-vigorous intensity physical activity (MVPA) is inversely associated with waist circumference and body mass index (BMI) among breast cancer survivors. Limited research has focused on behaviors that account for larger portions of the day [sleep, sedentary time, and light-intensity physical activity (LPA)]. We investigated the interdependent associations of self-reported sleep, objectively assessed prolonged and short bouts of sedentary time, total LPA, and total MVPA with waist circumference and BMI.

METHODS

A cross-sectional sample of breast cancer survivors (N = 256, mean age = 60 years; mean time since diagnosis = 3 years) wore an Actigraph GT3X+ accelerometer during waking hours for 7 days. Participants completed the Pittsburgh Sleep Quality Index and self-reported their waist circumference, height, and weight. An isotemporal substitution approach was used in linear regression models to explore the associations of reallocating time to sleep, sedentary and active behaviors on waist circumference, and BMI, after adjusting for potential confounders.

RESULTS

Reallocating 30 minutes to MVPA was significantly associated with lower waist circumference when allocated from sleep (-2.50 cm), prolonged sedentary time (-2.51 cm), or LPA (-2.71 cm). Reallocating 30 minutes of prolonged sedentary time to nonprolonged sedentary time was significantly associated with lower waist circumference (-0.94 cm). Similar results were observed for BMI.

CONCLUSIONS

Reallocating 30 minutes to MVPA was associated with significantly lower waist circumference and BMI, as was reallocating 30 minutes of prolonged sedentary time to 30 minutes of nonprolonged sedentary time.

IMPACT

Increasing MVPA levels and decreasing time spent in prolonged, unbroken sedentary bouts may be avenues for improving body composition in this population. Cancer Epidemiol Biomarkers Prev; 26(2); 254-60. ©2016 AACR.

Sedentary work and the risk of breast cancer in premenopausal and postmenopausal women: a pooled analysis of two case-control studies

OBJECTIVES

There is limited research on the association between sedentary behaviour and breast cancer risk, particularly whether sedentary behaviour is differentially associated with premenopausal and postmenopausal breast cancer. We pooled data from 2 case-control studies from Australia and Canada to investigate this association.

METHODS

This pooled analysis included 1762 incident breast cancer cases and 2532 controls. Participants in both studies completed a lifetime occupational history and self-rated occupational physical activity level. A job-exposure matrix (JEM) was also applied to job titles to assess sedentary work. Logistic regression analyses (6 pooled and 12 study-specific) were conducted to estimate associations between both self-reported and JEM-assessed sedentary work and breast cancer risk among premenopausal and postmenopausal women.

RESULTS

No association was observed in the 6 pooled analyses, and 10 of the study-specific analyses also showed null results. 2 study-specific analyses provided inconsistent and contradictory results, with 1 showing statistically significant increased risk of breast cancer for self-reported sedentary work among premenopausal women cancer in the Canadian study, and the other a non-significant inverse association between JEM-assessed sedentary work and breast cancer risk among postmenopausal women in the Australian study.

CONCLUSIONS

While a suggestion of increased risk was seen for premenopausal women in the Canadian study when using the self-reported measure, overall this pooled study does not provide evidence that sedentary work is associated with breast cancer risk.

Psychosocial Variables Related to Why Women are Less Active than Men and Related Health Implications

This article reviews psychosocial influences on women’s participation in physical activity as they differ from men and how associated activity differences impact women’s risk for a number of chronic diseases. This topic directly aligns with the mission of this special edition related to disparities in women’s health as the typically lower level of physical activity in females directly impacts their health. On average, females participate in physical activity at lower rates than their male counterparts. These lower rates of physical activity are directly related to both incidence of and outcomes from cardiovascular disease, type 2 diabetes, and breast and gynecological cancers. The relationship between psychosocial factors that are understood to affect physical activity differs between men and women. Specifically, self-efficacy, social support, and motivation are empirically substantiated factors that found to impact physical activity participation among women differently than men. Understanding these relationships is integral to designing effective interventions to target physical activity participation in women so that the related health risks are adequately addressed.

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.