The modifying effect of social class on the relationship between body mass index and breast cancer incidence

Early-life body mass index and risks of breast, endometrial, and ovarian cancers: a dose-response meta-analysis of prospective studies

BACKGROUND

The evidence for the associations between early-life adiposity and female cancer risks is mixed. Little is known about the exact shape of the relationships and whether the associations are independent of adult adiposity.

METHODS

We conducted dose-response meta-analyses of prospective studies to summarise the relationships of early-life body mass index (BMI) with breast, endometrial, and ovarian cancer risks. Pubmed and Embase were searched through June 2020 to identify relevant studies. Using random-effects models, the summary relative risks (RRs) and 95% confidence intervals (CIs) were estimated per 5-kg/m² increase in BMI at ages ≤ 25 years. A nonlinear dose-response meta-analysis was conducted using restricted cubic spline analysis.

RESULTS

After screening 33,948 publications, 37 prospective studies were included in this analysis. The summary RRs associated with every 5-kg/m² increase in early-life BMI were 0.84 (95% CI = 0.81-0.87) for breast, 1.40 (95% CI = 1.25-1.57) for endometrial, and 1.15 (95% CI = 1.07-1.23) for ovarian cancers. For breast cancer, the association remained statistically significant after adjustment for adult BMI (RR = 0.80, 95% CI = 0.73-0.87). For premenopausal breast, endometrial, and ovarian cancers, the dose-response curves suggested evidence of nonlinearity.

CONCLUSIONS

With early-life adiposity, our data support an inverse association with breast cancer and positive associations with ovarian and endometrial cancer risks.

The DNA damage repair landscape in Black women with breast cancer

BACKGROUND

Estrogen receptor positive (ER+) breast cancer is one of the most commonly diagnosed malignancies in women irrespective of their race or ethnicity. While Black women with ER+ breast cancer are 42% more likely to die of their disease than White women, molecular mechanisms underlying this disparate outcome are understudied. Recent studies identify DNA damage repair (DDR) genes as a new class of endocrine therapy resistance driver that contributes to poor survival among ER+ breast cancer patients. Here, we systematically analyze DDR regulation in the tumors and normal breast of Black women and its impact on survival outcome.

METHOD

Mutation and up/downregulation of 104 DDR genes in breast tumor and normal samples from Black patients relative to White counterparts was assessed. For DDR genes that were differently regulated in the tumor samples from Black women in multiple datasets associations with survival outcome were tested.

RESULTS

Overall, Black patient tumors upregulate or downregulate RNA levels of a wide array of single strand break repair (SSBR) genes relative to their white counterparts and uniformly upregulate double strand break repair (DSBR) genes. This DSBR upregulation was also detectable in samples of normal breast tissue from Black women. Eight candidate DDR genes were reproducibly differently regulated in tumors from Black women and associated with poor survival. A unique DDR signature comprised of simultaneous upregulation of homologous recombination gene expression and downregulation of SSBR genes was enriched in Black patients. This signature associated with cell cycle dysregulation (p < 0.001), a hallmark of endocrine therapy resistance, and concordantly, with significantly worse survival outcomes in all datasets analyzed (hazard ratio of 9.5, p < 0.001).

CONCLUSION

These results constitute the first systematic analysis of DDR regulation in Black women and provide strong rationale for refining biomarker profiles to ensure precision medicine for underserved populations.

Effect of long-term weight gain on the risk of breast cancer across women's whole adulthood as well as hormone-changed menopause stages: A systematic review and dose-response meta-analysis

Adult weight gain is a good indicator of excess body fatness for breast cancer risk. However, little is known about the effect of weight gain during other special periods in women's lifetime. A publication search in PubMed and Embase through April 2020 was conducted. A primary meta-analysis comparing the highest and lowest category and a secondary meta-analysis based on dose-response meta-analysis were performed to calculate risk estimates with 95% confidence intervals using a random-effects model. For postmenopausal breast cancer, the relative risk for highest vs. lowest category of adult weight gain and weight gain since menopause were 1.55 and 1.59 (RR = 1.55, 95% CI: 1.40, 1.71; RR = 1.59, 95% CI: 1.23, 2.05). For per 5 kg increase in adult weight gain, the summary RR of postmenopausal breast cancer was 1.08 (RR = 1.08, 95% CI: 1.07, 1.09), which is much stronger in Asian women (RR = 1.34, 95% CI: 1.22, 1.47). There was no significant finding among premenopausal women (RR = 1.00, 95% CI: 0.83, 1.21). Same as adult weight gain, weight gain since menopause might be an equivalent predictor for postmenopausal breast cancer risk. More studies are warranted to confirm the magnitude of this association further.

The association of neighborhood-level social class and tobacco consumption with adverse lung cancer characteristics in Maryland

INTRODUCTION

Although both active tobacco use and passive tobacco exposure are well-established as being risk factors for lung cancer, it is challenging to measure tobacco-related exposures at the population level, while considering other factors (gender, race, socioeconomic status) that may modify the relationship between tobacco and lung cancer. Moreover, research to date has focused primarily on relationships between tobacco and endpoints of lung cancer incidence or mortality. Tobacco's role in disease progression, through association with important disease characteristics such as tumor histological type and grade, and stage of disease at diagnosis, has been less well examined.

METHODS

This research examines associations between area-level tobacco use and social class, as well as individual gender, race and age, and three adverse disease characteristics (tumor type, grade and stage) among incident cases of lung cancer reported to the Maryland Cancer Registry in 2000. Cases were geocoded by residential address. Multi-level logistic regression models included Census block group-level estimates of per capita tobacco spending, from Consumer Expenditure Survey data, and a 4-item social class index, from Census estimates of rates of high school graduation, employment, white collar occupation, and per capita income.

RESULTS

Analyses of 3223 cases found no significant differences by race, however, results differed by gender. Lower block-group social class and higher tobacco spending were associated with squamous and small cell histological types and poorly differentiated or undifferentiated tumor grade. However, for later stage at diagnosis (SEER stages 2-7), both higher social class and greater tobacco spending were protective, especially for women, suggesting women in high tobacco use communities may benefit from early detection.

CONCLUSIONS

Results support using area-level behavioral data as tools for identifying high risk communities suitable for more resource-intensive research or interventions. Findings also suggest that area-level social resources are consistent drivers of lung cancer disparities, and merit continued research attention.

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.

Body fatness at a young age, body fatness gain and risk of breast cancer: systematic review and meta-analysis of cohort studies

Higher body fatness in adulthood has been consistently associated with an increased risk of postmenopausal breast cancer, as well as a tendency towards a lower risk of premenopausal breast cancer. However, the association between body fatness at a young age (≤30 years), body fatness gain and the risk of breast cancer is less defined. PubMed and Web of Science databases were searched to identify relevant publications. Risk estimates with 95% confidence intervals from each study were transformed into a continuous variable for each 5 kg m^-2 increase in body mass index (BMI) and were pooled under a random-effects model. Each 5 kg m^-2 increase in BMI was significantly associated with a 14%, 12% and 17% lower risk of breast cancer later in life among all women, premenopausal women and postmenopausal women, respectively. Significant heterogeneity and publication bias were observed. The results remained unchanged after the trim and fill method was applied to correct the bias. Each 5 kg m^-2 increase in BMI from a young age until cohort entry was significantly associated with a 13% and 14% higher risk of breast cancer in all women and postmenopausal women, respectively. In summary, higher body fatness at a young age may have a protective role in the later development of breast cancer in both premenopausal and postmenopausal women. However, this potential benefit should not be overemphasized, as our findings suggest that increased body fatness gain from a young age is positively associated with postmenopausal breast cancer risk. These findings further justify the need to maintain a steady weight throughout life.

Racial/Ethnic Differences in the Impact of Neighborhood Social and Built Environment on Breast Cancer Risk: The Neighborhoods and Breast Cancer Study

Background: Neighborhood socioeconomic status (nSES) has been found to be associated with breast cancer risk. It remains unclear whether this association applies across racial/ethnic groups independent of individual-level factors and is attributable to other neighborhood characteristics.Methods: We examined the independent and joint associations of education and nSES with odds of breast cancer. Residential addresses were geocoded for 2,838 cases and 3,117 controls and linked to nSES and social and built environment characteristics. We estimated ORs and 95% confidence intervals (CI) using multilevel logistic regression controlling for individual-level breast cancer risk factors and assessed the extent to which nSES associations were due to neighborhood characteristics.Results: Women living in the highest versus lowest nSES quintile had a nearly 2-fold greater odds of breast cancer, with elevated odds (adjusted ORs, 95% CI) for non-Hispanic whites (NHWs; 2.27; 1.45-3.56), African Americans (1.74; 1.07-2.83), U.S.-born Hispanics (1.82; 1.19-2.79), and foreign-born Hispanics (1.83; 1.06-3.17). Considering education and nSES jointly, ORs were increased for low education/high nSES NHWs (1.83; 1.14-2.95), high education/high nSES NHWs (1.64; 1.06-2.54), and high education/high nSES foreign-born Hispanics (2.17; 1.52-3.09) relative to their race/ethnicity/nativity-specific low education/low nSES counterparts. Adjustment for urban and mixed-land use characteristics attenuated the nSES associations for most racial/ethnic/nativity groups except NHWs.Conclusions: Our study provides empirical evidence for a role of neighborhood environments in breast cancer risk, specifically social and built environment attributes.Impact: Considering the role of neighborhood characteristics among diverse populations may offer insights to understand racial/ethnic disparities in breast cancer risk. Cancer Epidemiol Biomarkers Prev; 26(4); 541-52. ©2017 AACR.

Contextual Impact of Neighborhood Obesogenic Factors on Postmenopausal Breast Cancer: The Multiethnic Cohort

Background: While obesity is well-understood to increase breast cancer risk, the role of the neighborhood obesogenic environment, encompassing social and built environment attributes that influence body size, is poorly understood.Methods: Using principal components factor analysis, five composite factors [neighborhood socioeconomic status (nSES), urban, mixed-land development, unhealthy food environment, parks] on the basis of geospatial data were developed to characterize the obesogenic environment for 48,247 postmenopausal women in the Multiethnic Cohort, residing predominately in Los Angeles County. We used Cox proportional hazards regression to examine the association between neighborhood obesogenic factors and breast cancer risk (n = 2,341 cases after 17 years of follow-up), adjusting for body mass index (BMI), weight gain since age 21, education, established risk factors, other neighborhood factors, and clustering by block group.Results: Lower nSES was associated with lower breast cancer risk [quintile 1 vs. 5: HR, 0.79; 95% confidence interval (CI), 0.66-0.95], with a more pronounced association observed in Latinos (quintile 1 vs. 5: HR, 0.60; 95% CI, 0.43-0.85). More urban environments were associated with lower breast cancer risk in Japanese Americans (quintile 5 vs. 1: HR, 0.49; 95% CI, 0.26-0.90), and lower mixed-land development was associated with higher breast cancer risk in Latinos (quintile 1 vs. 5: HR, 1.46; 95% CI, 1.10-1.93).Conclusions: Obesogenic neighborhood environment factors, especially nSES, urbanicity, and mixed-land development, were differentially and independently associated with breast cancer risk in this multiethnic population.Impact: These findings highlight the need for additional studies of the driving contextual aspects of nSES that influence breast cancer risk. Cancer Epidemiol Biomarkers Prev; 26(4); 480-9. ©2017 AACRSee all the articles in this CEBP Focus section, "Geospatial Approaches to Cancer Control and Population Sciences."

The association of area-level social class and tobacco use with adverse breast cancer characteristics among white and black women: evidence from Maryland, 1992-2003

Background

In breast cancer, worse disease characteristics are associated with fewer social resources and black race. However, it is unknown whether social gradients have similar impact across race, and whether behaviors, including tobacco use, may explain a portion of the social gradient.

Methods

We modeled relationships between area-level social class, tobacco spending and tumor characteristics, using 50,062 white and black cases diagnosed from 1992–2003 in Maryland, a racially and economically diverse state on the east coast of the United States. Multi-level models estimated the effect of area-level social class and tobacco consumption on tumor grade, size, and stage at diagnosis.

Results

Adjusting for race, age and year of diagnosis, higher social class was associated with lower risk for tumors with histological grade 3 or 4 (O.R. 0.96, 95% C.I. 0.94,0.99), those diagnosed at SEER stage 2 or later (O.R. 0.89, 95% C.I. 0.86, 0.91), and tumor size >2 cm (O.R. 0.87, 95% C.I. 0.84, 0.90). Higher tobacco spending was associated with higher risk for higher grade (O.R. 1.01, 1.00, 1.03) and larger tumors (O.R. 1.03, 95% C.I. 1.01, 1.06), but was not statistically significantly related to later stage (O.R. 1.00, 95% C.I. 0.98, 1.02). Social class was less protective for black women, but tobacco effects were not race-specific.

Conclusions

Results suggest that in one U.S. geographic area, there is a differential protection from social class for black and white women, supporting use of intersectionality theory in breast cancer disparities investigations. Area-level tobacco consumption may capture cases’ direct use and second hand smoke exposure, but also may identify neighborhoods with excess cancer-related behavioral or environmental exposures, beyond those measured by social class. Given the growing global burden of both tobacco addiction and aggressive breast cancer, similar investigations across diverse geographic areas are warranted.

Cross-sectional study to assess the association of population density with predicted breast cancer risk

The Gail and CARE models estimate breast cancer risk for white and African-American (AA) women, respectively. The aims of this study were to compare metropolitan and nonmetropolitan women with respect to predicted breast cancer risks based on known risk factors, and to determine if population density was an independent risk factor for breast cancer risk. A cross-sectional survey was completed by 15,582 women between 35 and 85 years of age with no history of breast cancer. Metropolitan and nonmetropolitan women were compared with respect to risk factors, and breast cancer risk estimates, using general linear models adjusted for age. For both white and AA women, tisk factors used to estimate breast cancer risk included age at menarche, history of breast biopsies, and family history. For white women, age at first childbirth was an additional risk factor. In comparison to their nonmetropolitan counterparts, metropolitan white women were more likely to report having a breast biopsy, have family history of breast cancer, and delay childbirth. Among white metropolitan and nonmetropolitan women, mean estimated 5-year risks were 1.44% and 1.32% (p < 0.001), and lifetime risks of breast cancer were 10.81% and 10.01% (p < 0.001), respectively. AA metropolitan residents were more likely than those from nonmetropolitan areas to have had a breast biopsy. Among AA metropolitan and nonmetropolitan women, mean estimated 5-year risks were 1.16% and 1.12% (p = 0.039) and lifetime risks were 8.94%, and 8.85% (p = 0.344). Metropolitan residence was associated with higher predicted breast cancer risks for white women. Among AA women, metropolitan residence was associated with a higher predicted breast cancer risk at 5 years, but not over a lifetime. Population density was not an independent risk factor for breast cancer.

The enduring and evolving relationship between social class and breast cancer burden: a review of the literature

INTRODUCTION

Breast cancer in women has historically been seen as a "cancer of affluence" and there is a well-documented higher incidence among women of higher social class, as well as in societies with higher resources. However, the relationship between social class and breast cancer disease characteristics, especially those associated with poorer prognosis, is less well documented, and the overall relationship between breast cancer mortality and social class has been shown to vary. Furthermore, rapid changes in women's health and health-related behaviors in societies around the world may have an impact on both incidence and mortality patterns for breast cancer in the future.

METHODS

A PUBMED search on breast cancer and social class (incorporating the MeSH-nested concept of SES) yielded 403 possible studies published between 1978 and 2009, of which 90 met criteria for review. Our review discusses conceptualization and measurement of women's social class in each study, as well as findings related to breast cancer incidence, tumor biology or mortality, associated with social class.

FINDINGS

We found mostly consistent evidence that breast cancer incidence continues to be higher in higher social class groups, with some modification of risk with adjustment for known risk factors, including physical activity and reproductive history. However, biologic characteristics associated with poorer prognosis were negatively associated with social class (i.e., greater occurrence among disadvantaged women), and mortality from breast cancer showed inconsistent relationship to social class.

CONCLUSIONS

We discuss these studies in relation to the growing burden of breast cancer among low resource groups and countries, and the need for cancer control strategies reflecting the emerging demographics of breast cancer risk.