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2025
Rev Environ Health
This comprehensive systematic review and meta-analysis examined the relationship between exposure to DDT (a banned pesticide that persists in the environment and human body) and breast cancer by analyzing studies published from 2000 to 2021. The analysis found positive associations between DDT exposure and breast cancer risk across multiple study types: in long-term prospective studies, women with higher p,p’-DDT levels had 41% increased odds of breast cancer, while retrospective studies showed 15% increased odds with p,p’-DDE exposure and 33% increased odds with high p,p’-DDT concentrations. The strongest association was observed with o,p’-DDT exposure, showing 2.24 times higher odds of breast cancer. These findings support a positive relationship between DDT exposure and breast cancer risk, reinforcing the importance of maintaining the worldwide ban on DDT use, as this pesticide remains in human bodies for decades and continues to spread geographically even where it’s no longer applied.
2025
Sci Total Environ
This review examines the relationship between DEHP (a common plastic additive) and cancer development, noting that while epidemiological studies suggest a link between DEHP exposure and increased cancer risk, the specific mechanisms need further clarification. The research shows that DEHP influences multiple aspects of cancer biology, including cell growth, spread, and drug resistance, through various molecular pathways involving hormone receptors, inflammation, and genetic modifications. DEHP’s carcinogenic effects operate through complex mechanisms including PI3K/AKT signaling, estrogen receptor activation, and oxidative stress. Understanding these molecular pathways could help develop targeted strategies to prevent and treat cancers associated with DEHP exposure.
2025
Ecotoxicol Environ Saf
This study examined the link between cadmium (Cd) exposure and breast cancer risk using data from nearly 6,000 participants and a meta-analysis of 20 studies. The researchers found that higher cadmium levels significantly increased breast cancer risk, with the strongest association in estrogen receptor-positive (ER+) breast cancer subtypes, and identified glycated hemoglobin (HbA1c, a marker of blood sugar control) as a potential mechanism linking cadmium exposure to cancer development. The findings suggest that cadmium, an endocrine-disrupting metal found in the environment, may contribute to breast cancer through metabolic disruption. These results highlight the importance of reducing cadmium exposure and understanding how environmental toxins interact with metabolic health to influence cancer risk.
2024
Am J Epidemiol
This systematic review of 18 epidemiological studies evaluated whether exposure to PFAS—measured in blood or plasma—is associated with breast cancer risk. Across 11 of the studies included in the meta-analysis, higher concentrations of common PFAS such as PFOA and PFOS were not associated with increased breast cancer risk (per-log-unit RR for PFOA = 0.95, 95% CI: 0.77–1.18; PFOS = 0.98, 95% CI: 0.87–1.11). When analyses were restricted to studies where PFAS levels were measured before diagnosis, risk estimates were slightly higher (for PFOA: RR = 1.16, 95% CI: 0.96–1.40), but still not statistically significant. Overall, the evidence suggests that current PFAS exposures measured do not show a consistent link to breast cancer, though the authors note substantial study variability and the need for better prospective data.
2024
Med Lav
A meta-analysis of 23 cohort and case-control studies found that occupational benzene exposure was associated with an 8% increased breast cancer risk overall, with high-level benzene exposure showing a stronger 35% increased risk. The association was consistent for cancer incidence (8% increased risk) though not statistically significant for cancer mortality, and significant heterogeneity was detected across studies based on sex, publication year, study design, quality, and industry of employment. These findings suggest that benzene—a recognized carcinogen primarily studied in relation to leukemia—may also increase breast cancer risk in occupationally exposed workers, though the authors acknowledge that bias, confounding factors, and publication bias limit the strength of causal inference, highlighting the need for high-quality prospective studies with detailed exposure assessment to confirm these associations and inform workplace safety standards for the millions of workers potentially exposed to benzene in petroleum, chemical manufacturing, automotive repair, and other industries.
2024
Br J Cancer
This comprehensive meta-analysis of 63 studies found that women who never smoked but were exposed to secondhand smoke had a 24% increased risk of breast cancer, with the risk rising to 45% in some exposure settings. The breast cancer risk increased with greater exposure duration, intensity, and cumulative exposure—women exposed to secondhand smoke for 40 years had a 29% increased risk, while those exposed to the equivalent of 20 cigarettes per day had a 38% increased risk. The analysis showed the strongest associations for home exposure (17% increased risk) and combined home or workplace exposure (24% increased risk), demonstrating clear dose-response relationships where more exposure meant higher breast cancer risk. These findings are particularly important for public health policy because they show that even non-smokers face significant breast cancer risk from breathing others’ tobacco smoke, supporting the need for comprehensive smoke-free laws in homes, workplaces, and public spaces.
2023
Environ Sci Poll Res
This meta-analysis pooled data from 17 epidemiological studies to examine whether exposure to the dioxin compound 2,3,7,8-TCDD or to per- and polyfluoroalkyl substances (PFAS) is associated with breast cancer risk. The authors found evidence of a modest but statistically significant increased breast cancer risk associated with TCDD levels in the body,
2023
J Endocrinol Invest
A comprehensive literature review examining environmental endocrine-disrupting chemicals (EDCs) and hormone-related cancers concludes that several EDCs can be definitively classified as carcinogenic, including dioxin and cadmium for breast and thyroid cancer, arsenic and dioxin for prostate cancer, and organochlorines for testicular cancer. The review highlights that fetuses and newborns are most vulnerable to endocrine disruption, with adverse effects potentially manifesting at different ages throughout life, making it difficult to assess the full health impact of EDC exposure. The authors emphasize that EDCs represent a major environmental health issue requiring effective prevention policies, increased public awareness, and protective measures—particularly for pregnant women—along with standardized testing criteria to evaluate the carcinogenic potential of new chemicals before they enter widespread use.
2022
Crit Rev Food Sci Nutr
A systematic review of 131 epidemiological studies examining endocrine-disrupting chemicals (EDCs) and breast cancer risk found evidence that exposure to various EDCs—including pesticides (DDT/DDE, atrazine, dioxin), synthetic chemicals (BPA, phthalates, PFAS, PCBs, PBDEs), and other compounds found in everyday products—may elevate breast cancer risk, particularly when exposure occurs during early life. The review identified food as a major route of EDC exposure and emphasized that because most EDCs persist in the environment and accumulate in the body over time, long-term multi-generational health impacts need to be assessed. The authors call for improved exposure assessments of EDCs in food and food packaging, along with careful evaluation of their links to breast cancer development to inform policy-making and regulations aimed at protecting public health.
2022
Environ Sci Poll Res
This meta-analysis of 24 studies found that women occupationally exposed to organic solvents (chemicals used in manufacturing, cleaning, and industrial processes) had an 18% increased risk of breast cancer compared to unexposed workers, with the association being particularly strong in postmenopausal women (35% increased risk) and European workers. Organic solvents are commonly found in workplaces involving paint, adhesives, dry cleaning, and manufacturing, and the increased risk was consistent across both large cohort studies and case-control studies. These findings suggest that workplace exposure to organic solvents is an important and preventable occupational health hazard that contributes to breast cancer risk, especially for women working in industries that regularly use these chemicals.
2022
Am J Prev Med
A systematic review of five studies examining physical activity during adolescence and young adulthood in women with BRCA1/BRCA2 gene mutations found that higher activity levels may reduce or delay breast cancer risk later in life. Four of the five studies showed protective effects, with one specifically finding a 38% reduction in premenopausal breast cancer risk and another showing that active young women developed breast cancer at older ages. However, the limited number of studies and reliance on self-reported activity data suggest that while the findings are promising, more research is needed to confirm whether early-life physical activity can help protect BRCA mutation carriers from breast cancer.
2022
Cancers
This meta-analysis of nine studies involving over 33,000 women with BRCA1 or BRCA2 gene mutations. One significant finding was that women who first started using oral contraceptives at age 20 or older had a 21% increased risk of breast cancer compared to those who never used them. These findings suggest that the timing of oral contraceptive use may be important for women with BRCA mutations, though more research is needed to fully understand the relationship between hormonal contraception and cancer risk in genetic mutation carriers.
2022
Toxics
A meta-analysis of eight studies examining the relationship between PFAS chemicals and breast cancer found that two specific PFAS compounds—PFOA and PFHxS—were associated with significantly increased breast cancer risk, showing 32% and 79% elevated risk respectively. Surprisingly, PFNA showed a protective association with 24% reduced risk, while PFOS showed no association with breast cancer risk, though all findings had substantial statistical heterogeneity between studies. The researchers concluded that certain PFAS compounds may be potential breast cancer risk factors, with concerning evidence that even low-level exposures could have harmful impacts on human health, highlighting the need for further research to clarify the varied effects of different PFAS chemicals on breast cancer development.
2021
Environ Pollut
This meta-analysis synthesized data from 6 observational studies that used satellite-based measures of outdoor “light at night” (LAN) exposure to assess associations with breast cancer risk. Women in the highest-exposure group had were more likely to be diagnosed with breast cancer compared than those in the lowest-exposure group (OR = 1.11, 95% CI: 1.06–1.16). In subgroup analyses, the association remained significant for postmenopausal women (OR ≈ 1.07, 95% CI: 1.00–1.13).
2021
Sci Total Environ
This meta-analysis combined data from multiple studies to examine whether exposure to artificial light at night (LAN) — both outdoor and indoor — is associated with breast cancer risk. Women in the highest exposure categories had about a 12% greater risk of developing breast cancer compared with those in the lowest exposure categories (summary relative risk = 1.12, 95% CI: 1.06–1.18 for outdoor LAN; 1.13, 95% CI: 1.05–1.21 for indoor LAN). The association was somewhat stronger for estrogen-receptor–positive tumors. The authors concluded that LAN is a plausible, albeit modest, environmental risk factor for breast cancer.
2020
Curr Opin Urol
A systematic review identifying 22 cases of breast cancer in individuals on testosterone replacement therapy (TRT) found that 18 cases occurred in female-to-male (FtM) transgender individuals and only 4 in cisgender men, with testosterone treatment duration ranging from 5 weeks to 25 years at the time of diagnosis. The review noted a relatively higher incidence of breast cancer in FtM individuals on hormone therapy compared to cisgender men on TRT, though the small sample size prevents definitive conclusions about whether testosterone directly increases breast cancer risk or whether it should be contraindicated in those with prior breast cancer history. These findings highlight an important knowledge gap regarding the long-term cancer risks of gender-affirming hormone therapy and the need for larger, prospective studies to better understand the relationship between testosterone treatment and breast cancer development.
2020
Environ Res
A 24-year study of over 112,000 U.S. nurses found that women living within 10 kilometers (about 6 miles) of municipal solid waste incinerators had a 15% increased breast cancer risk compared to those not living near these facilities, with risk rising to 25% for women within 5 kilometers (3 miles). The association strengthened with longer duration of residence near incinerators and higher dioxin emission levels, and was consistent across hormone receptor subtypes and menopausal status. These findings provide evidence that residential exposure to dioxins—toxic chemicals released from waste incineration that persist in the environment and accumulate in the food chain—may increase breast cancer risk, highlighting the need for stricter emissions controls on incinerators and consideration of proximity to such facilities in community planning and cancer prevention strategies.
2018
Discov Oncol
This systematic review examined the relation of 4 neighborhood factors on breast cancer incidence and prognosis among African-American women: neighborhood socioeconomic status (nSES), residential segregation, spatial access to mammography, and residential pollution. The authors found that nSES, residential segregation and access to mammography were all related to stage at diagnosis, and nSES and living in more segregated areas were both associated with mortality. Residential pollution was not associated with increased risk of breast cancer in the studies reviewed.
2018
Eur J Epidemiol
This large international study pooling data from over 13,000 women across five countries found that night shift work increased breast cancer risk by 26% in pre-menopausal women, with the risk rising substantially for those working longer shifts (≥10 hours), more frequent nights (≥3 nights per week), or longer durations (≥10 years). Pre-menopausal women working both long durations and high frequency had a 2.5 times higher breast cancer risk, with current or recent night workers at higher risk than those who had stopped more than two years ago. Notably, no increased risk was found in post-menopausal women, and the elevated risk was primarily for estrogen receptor-positive tumors, particularly those that were also HER2-positive, suggesting that disruption of hormones and circadian rhythms during reproductive years may be key factors in how night work affects breast cancer risk.
2025
Saudi Med J
A systematic review and meta-analysis of 15 studies including 92,555 women found no evidence that hormonal fertility medications increase breast cancer risk, with pooled risk ratio analysis showing no association (RR=1.00, 95% CI: 0.97-1.02) and hazard ratio analysis initially suggesting a protective effect that became non-significant after accounting for study heterogeneity. The analysis revealed low heterogeneity in risk ratio studies but substantial heterogeneity in hazard ratio studies, which the authors attributed to methodological differences between studies rather than true variation in effects. These findings provide reassuring evidence for women considering or undergoing fertility treatment, though the authors caution that results should be interpreted carefully given the study heterogeneity and note that longer-term follow-up studies with standardized methodologies are needed to definitively establish the safety profile of hormonal fertility medications with respect to breast cancer risk, particularly for specific medication types, dosages, and treatment durations.
2025
Int J Hyg Environ Health
New research highlights the link between endocrine-disrupting chemicals (EDCs) and earlier breast development in girls. A systematic review of 68 studies found that 10 out of 14 high-quality studies linked prenatal and postnatal exposure to EDCs like organohalogenated compounds and phthalates to earlier thelarche. With thelarche now occurring nearly three months earlier per decade, these findings raise serious concerns about long-term health risks, including breast cancer. Reducing exposure to harmful chemicals in everyday products is crucial to protecting hormonal health and preventing early puberty.
2025
Global Health Res Pol
A meta-analysis of 17 observational studies found that the highest consumption of fast foods and ultra-processed foods (FFs/UPFs) was associated with a 25% increased breast cancer risk compared to the lowest consumption levels. The association was particularly strong in case-control studies and in Latin American populations, and remained significant regardless of sample size or BMI adjustment, though no association was found in cohort studies or when stratified by menopausal status. These findings suggest that diets high in ultra-processed foods—which often contain carcinogenic compounds formed during processing, additives, packaging contaminants, and unhealthy nutrient profiles—may contribute to breast cancer development, highlighting the urgent need for public health strategies and regulatory policies targeting food processing standards, marketing restrictions, improved labeling, and reduced accessibility of ultra-processed foods to reduce cancer risk, particularly as global consumption of these products continues to rise.
2025
Clin Transl Oncol
A review of 29 studies found that breast cancer patients have distinct imbalances in their gut and breast tissue bacteria that vary based on cancer type, stage, menopause status, body weight, and physical activity, though no single bacterial profile has yet emerged as a reliable biomarker. The research suggests that gut microbiome composition may influence how well breast cancer treatments work, with some beneficial bacteria and their metabolites potentially improving therapy effectiveness or slowing tumor growth. These findings highlight the microbiome as a promising new area for developing personalized breast cancer treatments and improving outcomes, though more research is needed to identify specific bacterial targets and understand the underlying mechanisms.
2025
Breast Cancer
A meta-analysis of 10 studies involving 1,730 women found that breast cancer patients had significantly lower gut bacterial diversity compared to healthy controls, with particularly pronounced differences in premenopausal women and women with normal body weight. The reduction in gut microbiome diversity—a marker of gut health—was not seen in overweight or obese women, suggesting body weight may influence the relationship between gut bacteria and breast cancer. These findings support the hypothesis that gut bacteria may play a role in breast cancer development, possibly through their influence on estrogen levels, though more research is needed to understand the underlying mechanisms and whether improving gut health could help prevent breast cancer.
2024
Int J Environ Res Public Health
A systematic review of 25 epidemiological studies (2013-2022) found that seven out of eight investigated outdoor air pollutants showed significant associations with increased breast cancer risk, with benzo[a]pyrene showing the strongest relationship. The review found that 100% of studies examining nitrogen oxides (NOₓ), 83% of PM₂.₅ studies, 69% of nitrogen dioxide (NO₂) studies, and 43% of PM₁₀ studies demonstrated positive associations with breast cancer risk, with hazard ratios ranging from 1.05-1.56 and odds ratios from 1.03-1.86, while ozone and cadmium showed negative or no associations. These findings strengthen the evidence that outdoor air pollution—particularly traffic-related pollutants and fine particulate matter—contributes to breast cancer development, though the authors note that further research is needed to establish causal mechanisms, particularly through epigenetic pathways, and acknowledge that the review’s focus on English-language articles from developed countries may limit generalizability.
2024
Sci Tot Environ
A comprehensive systematic review and meta-analysis of 28 studies including over 2.5 million individuals found that higher levels of outdoor artificial light at night (ALAN) were associated with a 12% increased breast cancer risk, though indoor ALAN showed a non-significant 7% increased risk, with no differences by menopausal status. For prostate cancer, the analysis suggested a 43% increased risk with outdoor ALAN exposure, though this was not statistically significant, and qualitative synthesis revealed positive associations with non-Hodgkin lymphoma, colorectal, pancreatic, and thyroid cancers. The authors note a critical limitation: most studies relied on low-resolution satellite imagery (1-5 km resolution from the Defense Meteorological Program) without information on light color or spectral composition, which may have led to exposure misclassification and underestimation of true effects, highlighting the urgent need for studies using higher-resolution exposure assessment methods and investigation of light pollution effects on cancers beyond breast cancer.
2024
Front Glob Women’s Health
A systematic review of 51 studies (2 RCTs and 49 observational studies) examined the association between modern contraceptive use and the risk of breast and reproductive cancers in women of reproductive age. The review found that hormonal contraceptive use significantly reduced the risk of ovarian cancer by 36% and endometrial cancer, while cervical cancer rates were lower among contraceptive users compared to non-users; notably, no increased breast cancer risk was found among healthy women (RR 1.00), but BRCA1/2 mutation carriers using oral contraceptives showed a 39% increased risk of breast cancer. These findings highlight the complex cancer-related effects of hormonal contraceptives: while they offer protective benefits against ovarian and endometrial cancers for most women, BRCA mutation carriers face elevated breast cancer risk, emphasizing the need for personalized contraceptive counseling that accounts for individual genetic risk factors. The study underscores the importance of healthcare providers considering family history and genetic profiles when discussing contraceptive options with women, particularly those with hereditary cancer susceptibility.
2024
Cancer Epidemiol Biomarkers Prev
While breast tissue was once thought to be sterile, the past decade has revealed it harbors unique bacterial communities, with growing evidence that breast tumor tissue has different microbiome compositions compared to healthy breast tissue. However, despite numerous studies examining breast cancer patients, research has been inconsistent in methodology and sample sizes, making it difficult to identify specific bacterial patterns reliably associated with breast cancer risk or outcomes. Only one large prospective study has linked breast microbiome composition to cancer prognosis, highlighting the need for larger, long-term studies to determine whether the breast microbiome could serve as a tool for predicting breast cancer risk, progression, or treatment response.
2024
Toxicol Lett
A meta-analysis of 15 studies including 3,468 cancer cases and 4,187 controls found that brominated flame retardant (BFR) exposure in adipose tissue was significantly associated with increased breast cancer risk, though no association was observed for thyroid cancer. The analysis revealed that BFR exposure generally elevates the risk of endocrine-related cancers, with BDE-28—a lower-brominated congener—showing particularly strong associations with increased cancer risk. These findings identify BFRs as a significant environmental risk factor for breast cancer and suggest that certain BFR congeners may be more carcinogenic than others, though the authors emphasize the need for further research to establish causal mechanisms and clarify how these ubiquitous flame retardant chemicals disrupt endocrine function to promote cancer development.
2024
Int J Mol Sci
This comprehensive review covers breast cancer biology from classification and risk factors through diagnosis and treatment, highlighting how the disease varies by subtype and between racial groups. The review examines both traditional factors like staging systems and molecular subtypes (Luminal A/B, Triple Negative, HER2-enriched) as well as emerging research on genetic mutations, epigenetic changes, and microbiome imbalances that may contribute to breast cancer development and progression. Recent evidence suggests that disruptions in the body’s microbial communities may play a role in breast cancer, with patterns potentially differing across populations, adding a new dimension to understanding racial disparities in breast cancer outcomes.
2024
Breast Cancer Res Treat
A meta-analysis of 10 randomized controlled trials including 14,282 participants and 591 breast cancers found that estrogen-alone hormone therapy was associated with a significant 23% reduction in breast cancer incidence (3.6% vs 4.7% in estrogen vs placebo groups, RR 0.77, 95% CI 0.65-0.91, P=0.002). This finding was driven primarily by the large Women’s Health Initiative trial but was supported by nine smaller trials showing similar directional effects, with estradiol formulations showing a 37% non-significant risk reduction. These results from randomized trials contradict findings from observational cohort studies and challenge conventional wisdom about hormone therapy and breast cancer, suggesting that estrogen-alone therapy (in women without a uterus) may actually protect against breast cancer rather than increase risk—a finding with important implications for counseling postmenopausal women about menopausal hormone therapy decisions.
2024
Environ Toxicol Pharmacol
A comprehensive review examines endocrine-disrupting chemicals (EDCs) classified as carcinogens—compounds recognized for decades as top priority toxicants and persistent organic pollutants due to their ability to disrupt endocrine signaling—analyzing their hazard identification, human exposure routes, carcinogenic potency, and mechanisms of action across different organs. The review discusses major endocrine-disrupting carcinogens and their cancer-causing potential while identifying critical research gaps, methodological bottlenecks, and limitations in analytical detection techniques. This analysis underscores the serious public health concern posed by EDCs with carcinogenic properties, highlighting the need for improved understanding of their mechanisms, better analytical methods for detection and measurement, and addressing research limitations to protect human health from these ubiquitous environmental contaminants that can both disrupt hormonal systems and initiate cancer development.
2024
Front Public Health
DDT, a highly persistent organochlorine pesticide comprising mainly p,p’-DDT (77%) and o,p’-DDT (15%), was widely used in agriculture and disease vector control with India being the primary consumer for malaria and leishmaniasis control, though global usage declined from ~5,388 metric tons annually (2001-2007) to ~3,772 metric tons (2008-2014) following the Stockholm Convention. As a xenoestrogen that bioaccumulates in fatty tissues and breast milk, DDT disrupts the endocrine system and enters the human circulatory system, causing reproductive toxicity, increased cancer risk (particularly threatening infants consuming contaminated breast milk), and carcinogenic effects, while also devastating wildlife populations through eggshell thinning in birds like pelicans and eagles. Prolonged DDT exposure causes cumulative toxicity that can alter morphogenesis, induce cancer, and cause reproductive system failure, yet its exceptional persistence and resistance to biodegradation means it continues to accumulate in the food chain and pose ongoing health threats despite reduced usage.
2024
Healthcare
This article highlights the disparities in the treatment of breast cancer based on various demographic factors. In terms of prevention and screening, people of minority groups such as African American and Hispanic women face challenges in accessing preventative measures like mammograms, mostly because of inequitable access to healthcare, financial constraints, and inadequate insurance coverage. These disparities also lead to delayed diagnoses and therefore worse outcomes in the treatment of these cancers. Additionally, provider bias, patient mistrust in the healthcare system, and systemic inequalities in the healthcare infrastructure cause inefficient treatment of breast cancer in these minority groups as well.
2023
Nutrient
A meta-analysis of 7 cohort studies and 17 case-control studies examining dietary isoflavone intake and breast cancer risk found a 29% reduced risk when comparing highest to lowest intake (OR=0.71; 95% CI: 0.72-0.81), with dose-response analysis showing that each 10 mg/day increase in isoflavone intake reduced breast cancer risk by 6.8% (cohort studies, OR=0.932; 95% CI: 0.90-0.96) and 11.7% (case-control studies), though no protective effects were detected at doses below 10 mg/day. The inverse association was independent of menopausal status and estrogen receptor status but varied by study design, being significant in case-control studies but not reaching significance in cohort studies alone. These findings provide evidence that dietary isoflavone intake—particularly from soy foods consumed in Asian populations—may reduce breast cancer risk in a dose-dependent manner starting at intake levels above 10 mg/day, supporting recommendations for dietary isoflavone consumption for breast cancer prevention.
2023
Adv Nutr
A systematic review and meta-analysis of 31 studies (29 included in quantitative analysis) following Cochrane methodology examined associations between healthy lifestyle indices (incorporating factors like healthy body weight, diet, physical activity) and breast cancer risk. Comparing the highest versus lowest adherence categories, the analysis found a 20% breast cancer risk reduction in prospective studies (HR=0.80; 95% CI: 0.78-0.83) and 26% reduction in retrospective studies (OR=0.74; 95% CI: 0.63-0.86), with inverse associations remaining significant when stratified by menopausal status (except for premenopausal BC in prospective studies) and across molecular subtypes: ER+/PR+ (HR=0.68; 95% CI: 0.63-0.73), ER+/PR- (HR=0.78; 95% CI: 0.67-0.90), and ER-/PR- (HR=0.77; 95% CI: 0.64-0.92). These findings—with most studies scoring low risk of bias and moderate certainty of evidence—demonstrate that adherence to healthy lifestyles reduces breast cancer risk by approximately 20-30% regardless of molecular subtype or menopausal status, supporting the prioritization of lifestyle-based recommendations for population-level breast cancer prevention as a key modifiable approach to reducing the substantial disease burden.
2023
Cancer Epidemiol Biomark Prev
A systematic review and meta-analysis of 34 observational studies and 3 Mendelian randomization studies found that women with the highest levels of C-reactive protein (CRP)—a marker of systemic inflammation—had a 13% increased breast cancer risk compared to those with the lowest levels, though the quality of evidence was rated as very low to moderate. While adiponectin showed a protective association (24% reduced risk), this finding was not supported by genetic evidence from Mendelian randomization studies, and there was little evidence that other inflammatory markers like TNFα and IL-6 affected breast cancer risk. These findings suggest that while chronic low-grade inflammation measured by CRP may modestly increase breast cancer risk, the overall role of inflammation in breast cancer development remains unclear, with limited support beyond CRP—highlighting the need for higher-quality prospective studies and mechanistic research to clarify whether inflammation is truly causal or merely a marker of other underlying processes that drive breast carcinogenesis.
2023
Frontiers
A meta-analysis of 21 studies including 734,372 participants worldwide found that light at night (LAN) exposure was associated with a 12% increased breast cancer risk overall, with case-control studies showing 16% increased risk and cohort studies showing 8% increased risk. The association was particularly pronounced in Asian populations (24% increased risk) and for ER-positive breast cancers (10% increased risk), while outdoor LAN specifically showed a 7% increased risk. These findings support the hypothesis that artificial light exposure at night disrupts circadian rhythms and suppresses melatonin production—a hormone with anti-cancer properties—though the authors caution against taking melatonin supplements for prevention without medical advice until mechanisms are better understood, and emphasize the need for high-quality research accounting for environmental confounding factors to clarify the role of light pollution in breast cancer development.
2023
Environ Res
A meta-analysis of 17 epidemiological studies examining cadmium exposure and breast cancer risk found no statistically significant associations overall or when examining specific exposure routes separately (dietary cadmium or biomarker-based studies), with substantial heterogeneity between studies and no clear patterns by menopausal status. The inconclusive findings leave critical questions about whether specific exposure routes (occupational, air pollution, smoking) pose different risks than dietary intake or whether residual confounding by tobacco smoke constituents may influence observed associations. These results highlight the need for future research with better exposure assessment methods that can distinguish between different cadmium sources and routes of exposure, particularly occupational and environmental air pollution exposures that may be more relevant than diet for populations living near industrial areas where cadmium contamination is prevalent.
2023
J Epidemiol
A comprehensive systematic review and meta-analysis of 169 observational studies published through January 2020 examined the association between cigarette smoking and breast cancer risk using random-effects models and dose-response analyses. The pooled analysis found that current smokers had 7% increased breast cancer risk, former smokers 8% increased risk, and ever smokers 9% increased risk compared to never smokers, with results consistent across both case-control and cohort studies and across most covariates including genetic mutations (BRCA) and relevant polymorphisms. Importantly, breast cancer risk increased in a linear dose-response manner with both smoking intensity (12% increased risk for 20 cigarettes/day, 26% for 40 cigarettes/day) and duration (5% increased risk for 20 years, 11% for 40 years), demonstrating clear dose-response relationships. This large and comprehensive meta-analysis, which employed innovative search methods, provides strong evidence supporting a causal role of tobacco smoking in breast cancer development, resolving previous controversy on this association and establishing smoking as a modifiable risk factor for breast cancer with risks increasing proportionally to the amount and duration of smoking exposure.
2023
Reprod Toxicol
A review of epidemiologic literature examining environmental chemical exposures during pregnancy and three maternal health outcomes (preeclampsia, gestational diabetes, and breast cancer) found that pregnancy represents a unique critical period when biological changes can heighten women’s susceptibility to chemicals from air, food, water, and consumer products—including flame retardants, plasticizers, pesticides, and lead—though research has disproportionately focused on fetal outcomes rather than maternal health risks, which remain poorly characterized for most chemicals. While evidence shows that lead exposure increases risk of pregnancy-induced hypertensive disorders and pregnancy can amplify women’s vulnerability to environmental chemicals, variations in study design, exposure assessment methods, and inconsistent adjustment for confounders limited comparability across studies. The authors emphasize that future research must recognize pregnancy as a critical window for women’s lifelong health, calling for incorporation of biomarkers of exposure and effect, deliberate timing and methods of measurement, and consistent confounder adjustment to strengthen understanding of the pregnancy exposome and its impacts on maternal health outcomes beyond the immediate postpartum period.
2023
Foods
A review of regulations for endocrine-disrupting chemicals and persistent organic pollutants in infant formula found that while breast milk remains the healthiest option, infant formula must be strictly monitored to ensure it is pollutant-free, particularly given the vulnerability of newborns to chemical exposures. Current regulations and upper limits for contaminants in infant formula vary worldwide, though standardized policies exist to protect infants, and continuous monitoring is required to maintain safety standards. The authors emphasize that risk assessment studies are limited but urgently needed to better understand exposure variations and evaluate the health risks infants face from dietary exposure to pollutants during this critical developmental period.
2023
Environ Sci Technol
This review investigates the migration of bisphenols and alternative color developers from thermal labels on cling-wrapped fresh food, identifying them as significant dietary sources of these compounds. While no BPA was found in packaging, high concentrations of bisphenol S (BPS) and other alternatives were detected, particularly in thermal labels. Migration studies revealed that BPS and related compounds leach into food, especially fish, raising potential health concerns. These findings highlight the need for further risk assessments regarding these alternative chemicals in food packaging due to past findings about BPA being an endocrine disruptor. This will help mitigate exposure risks and ensure consumer safety.
2023
Frontiers
This meta-analysis aimed to evaluate the association between exposure to endocrine-disrupting chemicals (EDCs), including phthalates and other common environmental pollutants, and breast cancer risk. The study found that certain EDCs—such as p,p′-DDT, chlordane, HCH, and specific PCBs—were positively associated with increased breast cancer risk, while a few compounds like BBP and PFDoDA showed a negative association.
2023
Cancer Causes Control
A review examining how low socioeconomic status (SES) contributes to early chronic disease onset and reduced life expectancy found that neighborhood-level factors—including environmental pollutants, deprivation, social isolation, structural racism, and discrimination—create chronic life stress that affects molecular processes like DNA methylation, inflammation, and immune response, contributing to more aggressive tumor biology, particularly in Black Americans. Despite decades of research showing associations between neighborhood factors and cancer outcomes in marginalized communities, the biological mechanisms linking SES to cancer disparities remain poorly understood, though emerging evidence suggests chronic stress pathways may play a central role. The authors summarize current methods for measuring neighborhood-level deprivation, discrimination, and structural racism in cancer disparities research and recommend adopting a multi-faceted intersectional approach to reduce cancer health inequities and develop effective interventions promoting health equity.
2022
J Occup Environ Med
A systematic review and meta-analysis of 9 studies found that female flight attendants had a 43% increased breast cancer incidence compared to the general population, but surprisingly, neither cosmic radiation exposure nor circadian rhythm disruption—the two primary occupational hazards hypothesized to drive this excess risk—showed clear associations with breast cancer in the available studies. Three studies suggested a possible link with cosmic radiation while none found associations with circadian disruption, leaving the underlying cause of the elevated breast cancer risk among flight attendants unexplained. These findings highlight a critical gap in occupational health research: while flight attendants clearly face elevated breast cancer risk, the mechanisms remain unclear, potentially involving unmeasured factors such as reproductive patterns (delayed childbearing, fewer children), lifestyle factors associated with the profession, cumulative effects of multiple low-level exposures, or limitations in exposure assessment methods—underscoring the urgent need for studies with detailed individual-level data on occupational exposures, work schedules, and lifestyle factors to identify modifiable risk factors for this vulnerable workforce.
2022
Nutr Cancer
An updated meta-analysis of 21 studies including over 346,000 participants found that the most pro-inflammatory diets were associated with a 16% increased breast cancer risk overall, with particularly strong associations among postmenopausal women (13% increased risk), obese women with BMI ≥30 kg/m² (35% increased risk), and populations in developing countries (79% increased risk). The analysis revealed important methodological influences on effect estimates, with stronger associations observed in case-control studies (50% increased risk), studies using hospital-based controls (111% increased risk), and cohort studies with prolonged follow-up (13% increased risk). These findings not only confirm that pro-inflammatory dietary patterns increase breast cancer risk but also demonstrate that the magnitude of association varies substantially by population characteristics and study design, with obesity and postmenopausal status appearing to amplify the carcinogenic effects of inflammatory diets—suggesting that anti-inflammatory dietary interventions may be particularly beneficial for overweight/obese postmenopausal women and populations in developing countries where rapid dietary transitions toward processed, inflammatory foods are occurring.
2022
Crit Rev Food Sci Nutr
This systematic review of 131 epidemiological studies evaluated the association between various endocrine-disrupting chemicals, including phthalates and hormonal exposures like contraceptive pills, and the risk of breast cancer. It found that several EDCs, particularly phthalates and oral contraceptive use, were consistently associated with increased breast cancer risk across multiple studies.
2022
Front Endocrinol
A meta-analysis of 8 studies (5 cohort and 3 case-control studies) examined whether fertility treatments increase breast cancer risk in genetically susceptible women, including those with a family history of breast cancer or BRCA mutations. The analysis found no significant increase in breast cancer risk associated with fertility treatments in genetically susceptible women overall (OR 1.18), women with a family history of breast cancer (OR 1.35), or BRCA mutation carriers (OR 1.02), with similarly reassuring results across subgroups including BRCA1 carriers, BRCA2 carriers, and women treated with specific fertility medications like in vitro fertilization, clomiphene citrate, or gonadotropins. This first meta-analysis on this topic provides reassuring evidence that fertility treatments do not significantly increase breast cancer risk even in women with hereditary susceptibility, though the authors note that larger prospective studies with more detailed information are needed to fully understand potential risks. Future research should examine whether risks vary by breast cancer subtype, explore the genetic mechanisms underlying hormone-related breast cancer, and investigate the relationship between BRCA mutations and hormone receptor-positive breast cancer specifically.
2022
Carcinogen
A meta-analysis of 12 breast cancer studies and 8 ovarian cancer studies in women with BRCA1 or BRCA2 mutations found that oral contraceptive (OC) use was associated with a 24% increased breast cancer risk but a 47% decreased ovarian cancer risk. The increased breast cancer risk was observed only with long-term OC use (>5 years), while the ovarian cancer protection occurred regardless of duration, and these patterns were consistent when BRCA1 and BRCA2 carriers were analyzed separately. These findings present a complex risk-benefit trade-off for BRCA mutation carriers considering oral contraceptives, suggesting that while OCs provide substantial protection against ovarian cancer—a particularly deadly cancer in this high-risk population—they also modestly increase breast cancer risk with prolonged use, requiring careful individualized counseling about contraceptive choices and cancer prevention strategies.