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2019
Environ Int
This 20-year study of 748 women diagnosed with breast cancer in North Carolina found that those with the highest levels of DDE (a breakdown product of the banned pesticide DDT) in their blood had nearly twice the risk of death compared to those with the lowest levels. The association between DDE exposure and breast cancer death was particularly strong among Black women and women with estrogen receptor-negative tumors, with Black women showing more than double the mortality risk. Since DDT was banned in the U.S. in 1972 but DDE persists in the environment and body fat for decades, these findings suggest that legacy pesticide exposure may contribute to worse breast cancer outcomes and racial disparities in breast cancer survival.
2019
Occ Environ Med
This Canadian study of over 2,200 women found that occupational exposure to polycyclic aromatic hydrocarbons (PAHs)—chemicals released from burning materials like coal, oil, and gasoline—increased breast cancer risk by 32%, with higher risks seen in women exposed to high levels for more than 7 years. The association was particularly strong among women with a family history of breast cancer, where prolonged high exposure nearly tripled the risk. These findings suggest that workplace PAH exposure may be an important and preventable breast cancer risk factor, especially for women with genetic susceptibility to the disease.
2019
Int J Cancer
A large prospective study of 182,145 women in the Nurses’ Health Study found that higher fruit and vegetable consumption was associated with an 11% lower risk of invasive breast cancer, with the strongest benefits from cruciferous vegetables (like broccoli and cabbage) and yellow/orange vegetables (like carrots and squash). Women consuming more than 5.5 servings per day had significantly lower breast cancer risk compared to those eating 2.5 servings or less, with particularly strong protective effects against aggressive tumor types including estrogen receptor-negative (16% risk reduction per 2 additional servings/day), HER2-enriched (21% reduction), and basal-like (16% reduction) breast cancers. The protective associations were most pronounced for tumor subtypes that tend to be more aggressive and harder to treat. These findings suggest that a diet rich in fruits and vegetables, especially cruciferous and yellow/orange varieties, may help prevent breast cancer and particularly reduce the risk of developing more aggressive forms of the disease.
2019
J Work Environ Health
A prospective study of 16,084 Swedish women found that occupational exposure to chemicals was associated with a 26% increased risk of postmenopausal breast cancer, with risk increasing based on duration of exposure. Women exposed to diesel exhaust for more than 10 years showed a 69% increased risk, while exposure to organic solvents showed a non-significant elevated risk. The researchers estimated that occupational chemical exposures accounted for 2% of all breast cancer cases in this population, highlighting workplace chemical exposure as a potentially important but often overlooked risk factor for breast cancer.
2019
Am J Clin Nutr
A large French cohort study of 76,442 women over age 50 followed for 11 years found that current soy supplement use was associated with a 22% reduced risk of estrogen receptor-positive (ER+) breast cancer but a 101% increased risk of ER-negative breast cancer compared to never users. The risk profile varied significantly by personal characteristics: women with a family history of breast cancer showed a 36% increased risk with soy supplement use, while those without family history showed an 18% reduced risk; premenopausal or recently postmenopausal women showed a 50% risk reduction, while women more than 5 years past menopause showed a 6% increased risk. These findings suggest that soy supplements—often marketed as natural alternatives to hormone therapy—may have complex and opposing effects on breast cancer risk depending on tumor biology and individual characteristics, cautioning against their use particularly in women with breast cancer family history.
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.
2018
Am J Epidemiol
A cohort study of 4,503 female autoworkers in Michigan exposed to metalworking fluids (MWFs)—oil and chemical mixtures used in metal manufacturing—found that increased exposure to straight mineral oil MWFs was associated with a 13% increased breast cancer risk per interquartile range increase in cumulative exposure. Among younger women who developed premenopausal breast cancer, exposure to synthetic MWFs (chemical lubricants without oil) showed elevated risk, suggesting potentially different carcinogenic mechanisms in younger versus older women. This occupational study addresses a critical gap in breast cancer research by providing quantitative exposure-response data for a specific chemical mixture affecting a large workforce, offering one of the few leads on modifiable environmental risk factors for breast cancer.
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
Scand J Work Environ Health
A European multicenter case-control study of 104 male breast cancer cases and 1,901 controls found that high cumulative lifetime exposure to trichloroethylene (>23.9 ppm-years) was associated with a 110% increased male breast cancer risk compared to non-exposure, with the association persisting when only exposures occurring 10 or more years before diagnosis were considered, indicating a true latency effect. The study also suggested possible roles for benzene and ethylene glycol in male breast cancer risk, though no clear dose-response relationships were observed for these chemicals. These findings are particularly important given that male breast cancer is rare, often diagnosed at later stages, and has worse prognosis than female breast cancer, and they add to evidence that occupational solvent exposures—particularly trichloroethylene used in metal degreasing, dry cleaning, and industrial cleaning—may be underrecognized risk factors for breast cancer in both men and women, warranting stricter workplace exposure limits and enhanced surveillance of workers in high-exposure industries.
2018
Environ Res
A Chinese case-control study of 209 breast cancer patients and 165 controls found that women with the highest levels of PBDE flame retardants in their adipose tissue had dramatically elevated breast cancer risk, with some congeners showing 447% to 545% increased risk in the highest exposure groups compared to the lowest. Most individual PBDE congeners—including BDE-47, BDE-99, BDE-100, BDE-209, and total PBDEs—were significantly higher in breast cancer cases than controls (median 95.0 vs 73.7 ng/g lipid) and showed strong dose-response relationships with increasing exposure levels. The associations remained robust for estrogen receptor-positive breast cancers and in multivariate models adjusting for age and reproductive factors, providing compelling evidence that PBDE exposure may play an important role in breast cancer development, particularly in populations with high environmental exposures to these persistent flame retardant chemicals.
2018
Breast Cancer Res
A nationwide study of 22,466 Danish female nurses found that long-term exposure to road traffic Noise was associated with increased breast cancer risk, particularly for hormone receptor-positive tumors. For every 10-decibel increase in 24-year average Noise levels at their residence, women showed a 23% increased risk of estrogen receptor-positive (ER+) breast cancer and a 21% increased risk of progesterone receptor-positive (PR+) breast cancer, with no significant association for hormone receptor-negative tumors. The association was especially strong among nurses who worked night shifts, showing a 236% increased risk of ER+ breast cancer compared to a 21% increase in those not working nights. These findings suggest that chronic traffic Noise exposure may contribute to breast cancer development, potentially through stress-related hormonal pathways, with night shift work potentially amplifying this risk.
2018
Int J Psychiatry Med
A hospital-based study of 250 breast cancer patients and 250 controls in Turkey found that recent major stressors—particularly those occurring within the last five years—were associated with a 372% increased risk of breast cancer (the strongest factor identified). Other significant risk factors included inadequate social support (83% increased risk), loss of a father during childhood (168% increased risk), family history of cancer (55% increased risk), and history of psychiatric disorders (95% increased risk), suggesting that psychological trauma and social factors may play substantial roles in breast cancer development alongside genetic predisposition.
2018
Cancer Epidemiol Biomarkers Prev
This study examined how exposure to endocrine-disrupting chemicals (EDCs) during puberty affects breast tissue development in 200 Chilean girls by measuring urinary concentrations of phenols and phthalates at two stages of breast development and assessing breast density. The researchers found that certain phthalate metabolites were associated with increased breast density measures – specifically, higher levels of monocarboxyisooctyl phthalate were linked to 7% higher percent dense breast tissue, and monoethyl phthalate was associated with increased fibroglandular volume. Bisphenol A showed a U-shaped relationship with fibroglandular volume, where girls with middle-level exposures had at least 10% lower fibroglandular volume compared to those with low or high exposures. The findings suggest that developing breast tissue is vulnerable to certain EDCs during childhood and adolescence, which may have implications for future breast cancer risk since breast density is a known risk factor.
2018
Environ Health
This longitudinal study examined how exposure to endocrine disrupting chemicals (EDCs) affects the timing of menarche in Chilean girls by measuring 26 phenol and phthalate compounds in urine samples collected before breast development and during adolescence. The researchers found that different chemicals had varying effects depending on when exposure was measured: higher early exposure to DEHP was associated with later menarche, while early exposure to certain phenols and later exposure to some phthalates were linked to earlier menarche. The study also revealed that body weight influenced these effects, with overweight or obese girls showing earlier menarche when exposed to higher levels of certain chemicals like triclosan, while normal-weight girls did not show this association. These findings demonstrate that specific EDCs can disrupt normal sexual development in girls, with timing of exposure and body weight being important factors.
2000
Am J Indust Med
This Danish nationwide study of 230 male breast cancer cases found that men occupationally exposed to gasoline and its combustion products had a 2.5 times higher risk of breast cancer, with the risk rising to 5.4 times higher among men first exposed before age 40. Gasoline contains several known carcinogens including benzene and produces cancer-causing combustion products, which may explain this elevated risk. Since male breast cancer is rare but shares similar biology with female breast cancer, these findings suggest that gasoline exposure may also increase breast cancer risk in women and warrant further investigation in female workers.
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
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
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
Sci Rep
A secondary analysis of 15,536 post-menopausal women from the Alberta Tomorrow Project cohort examined whether exposure to traffic-related air pollution (TRAP), measured using nitrogen dioxide (NO₂) levels, was associated with breast cancer risk over 12.6 years of follow-up during which 523 breast cancer cases were diagnosed. After adjusting for confounders including age, education, births, diet, income, physical activity, BMI, and smoking, the study found no significant association between NO₂ exposure and post-menopausal breast cancer risk (HR = 1.10 per 10-ppb increase in NO₂; 95% CI = 0.90, 1.34). The authors suggest that while the magnitude of risk observed was similar to other studies, the lack of statistical significance may be due to the study’s sample size limitations and the fact that NO₂ levels in Alberta are lower than in many other regions globally where associations have been found. These findings indicate that traffic-related air pollution may not significantly impact post-menopausal breast cancer risk in regions with relatively low pollution levels, though larger studies in more polluted areas may be needed to fully assess this relationship.
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
Ecotoxicol Env Saf
A Mendelian randomization study using genetic data from European populations found that specific endocrine-disrupting chemicals (EDCs) were causally associated with different breast cancer subtypes: n-butyl paraben (n-BuP) increased Luminal A risk, mono-methyl phthalate decreased Luminal B risk, and mono-iso-butyl phthalate (MiBP) increased triple-negative breast cancer risk. Mediation analysis revealed that blood metabolites—including caffeic acid sulfate and caffeine metabolism ratios—partially explained the n-BuP effect on Luminal A, while methylsuccinate mediated the MiBP effect on triple-negative cancer, and epigenetic analysis identified specific DNA methylation sites associated with EDC exposure and breast cancer risk. These findings provide the first genetic evidence suggesting causal relationships between specific EDC exposures and breast cancer subtypes through distinct metabolic and epigenetic pathways, identifying potential biomarkers for early detection and highlighting the heterogeneous effects of different EDCs on breast cancer biology—underscoring the need for chemical-specific and subtype-specific prevention strategies rather than treating all EDCs or breast cancers as uniform entities.
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.
2025
Epidemiol
A prospective study of 46,150 Sister Study participants followed for a median 13.4 years (4,155 breast cancer cases) used EPA Toxics Release Inventory data to quantify residential air emissions of 28 industrial compounds—many carcinogenic or endocrine-disrupting—during the 10 years before enrollment (2003-2006). Emissions within 3 km of residences showed non-significant associations with breast cancer for nickel compounds (HR = 1.3; 95% CI: 1.0-1.6 for highest vs. no exposure) and trichloroethylene (HR = 1.3; 95% CI: 1.0-1.6), while exposure continuum mapping identified 25 mixture profiles explaining 72% of emissions variance, with the joint-exposure response function suggesting higher breast cancer incidence among individuals with rare, high-emission profiles, though the overall mixture trend was not statistically significant (p = 0.09). These findings indicate that residential proximity to industrial air emissions of certain carcinogens—particularly nickel compounds and trichloroethylene—may be associated with increased breast cancer risk, though the lack of overall mixture association may reflect that individual compounds or specific emission sources are more important than cumulative exposure profiles, or that most participants experienced relatively low emissions with elevated risks concentrated among small subgroups with high exposure to specific pollutants.
2025
Sci Rep
A large U.S. study of 4,455 people found that exposure to triclosan (TRS)—an antibacterial chemical commonly found in soaps, toothpaste, and personal care products—was associated with more than double the risk of breast cancer at moderate exposure levels, with the relationship following an inverted U-shape pattern. The association was strongest among overweight individuals, people under 60 years old, and white participants, while other tested chemicals (including bisphenol A, benzophenone-3, and parabens) showed no significant link to breast cancer risk. These findings suggest that triclosan exposure may be an important modifiable risk factor for breast cancer, particularly for certain population groups, though more research is needed to understand the underlying mechanisms and confirm causality.
2025
JAMA Netw Open
A cross-sectional study of 121 Black and White women with breast cancer found that chronic stressors—including perceived stress, inadequate social support, discrimination, and neighborhood deprivation—were associated with harmful immune and tumor changes, with particularly pronounced effects in Black women who also lived in significantly more socioeconomically deprived neighborhoods. Higher stress, discrimination, and neighborhood deprivation were linked to increased systemic inflammation, immune-suppressive tumor environments (including tumor-promoting M2 macrophages), and elevated tumor mutational burden, while greater social support was associated with beneficial immune-stimulatory changes including increased natural killer cells in breast tissue. Black women showed distinct stress-related immunologic signatures including enhanced chemotaxis, immune suppression at the systemic level, and increased tumor-associated myeloid cells, suggesting that chronic psychosocial and environmental stressors may biologically contribute to breast cancer disparities by creating a pro-tumorigenic immune environment—findings that underscore the urgent need for interventions addressing social determinants of health as cancer prevention strategies.
2025
Int J Environ Res Public Health
A prospective study of 10,305 women in Nova Scotia found that frequent sleep trouble (“all of the time”) was associated with a 141% increased breast cancer risk, while high physical activity was associated with a 42% reduced risk. Interestingly, sleep duration itself showed no association with breast cancer risk, suggesting that sleep quality—rather than quantity—may be the more important factor. These findings add sleep disturbances to the list of modifiable lifestyle risk factors for breast cancer and reinforce the protective benefits of physical activity, though the authors note that further research is needed to understand the biological mechanisms linking poor sleep quality to increased cancer risk.
2025
Nutr J
A prospective cohort study of 13,567 Chinese women followed for nearly 15 years found that consuming one or more servings of sugar-sweetened beverages (SSBs) per week was associated with a 58% increased breast cancer risk compared to consuming less than one serving weekly. The association was partly mediated by body mass index (4.2%) and uric acid (18.8%), with genetic analyses identifying additional metabolic mediators including cholesterol and fatty acid ratios accounting for small portions of the effect. Interestingly, higher soy milk consumption (3-6 portions weekly) was associated with a 69% reduced breast cancer risk, while dairy milk showed a non-significant trend toward increased risk, and no associations were found for juice, coffee, tea, or alcohol, suggesting that reducing SSB consumption and addressing the associated metabolic disruptions could be effective breast cancer prevention strategies.
2025
J Exp Sci Environ Epidemiol
A nationwide US study analyzing drinking water contamination and cancer incidence (2016-2021) found that PFAS (“forever chemicals”) in public water systems were associated with increased rates of multiple cancers, with incidence rate increases ranging from 2% to 33% across different cancer types. The strongest association was a 33% increased rate of oral cavity and pharyngeal cancers linked to PFBS exposure, with other significant associations found for digestive, respiratory, endocrine, thyroid, urinary, brain, and soft tissue cancers, showing notable sex-based differences in cancer patterns. Researchers estimate that PFAS contamination in US drinking water may contribute to approximately 4,600-6,900 new cancer cases annually, underscoring the urgent public health need for stricter water quality standards and expanded monitoring of these persistent environmental pollutants.
2025
Int J Environ Sci
This study investigated how DEHP (a common plastic additive) affects triple-negative breast cancer (TNBC), the most aggressive form of breast cancer. The researchers found that prolonged DEHP exposure enhanced cancer cell migration and invasion both in laboratory cultures and in animal models by activating a specific protein pathway involving MSI2, which promotes cancer spread and stem cell-like properties. DEHP exposure also reduced levels of a protective microRNA (miR-155-5p), while increasing MSI2 expression, suggesting these molecules work in opposition to each other. The findings identify MSI2 as a potential therapeutic target and prognostic marker for TNBC patients, providing new insights into how plastic additives may contribute to cancer metastasis.
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
Environ Health Perspect
Researchers analyzed 279 chemicals known to cause mammary tumors in rodents and identified 642 additional chemicals that activate estrogen or progesterone signaling, finding that tumor-causing chemicals were significantly more likely to stimulate hormone production, activate estrogen receptors, or damage DNA—characteristics that likely increase breast cancer risk in humans. The study found that more mammary carcinogens worked by increasing hormone production than by directly activating estrogen receptors, with chemicals showing stronger hormone-disrupting effects being most likely to cause tumors, demonstrating a clear dose-response relationship. These findings suggest that hundreds of chemicals currently in use may pose unrecognized breast cancer risks and should not be assumed safe without specific testing for breast effects, with the strongest evidence chemicals prioritized for exposure reduction and improved testing methods needed to identify additional hazardous substances. The research provides a framework for identifying and regulating chemicals that may contribute to breast cancer through hormone disruption and genetic damage—mechanisms supported by both animal and human studies.
2024
Cancer Med
A mouse study found that exposure to bacterial toxins (lipopolysaccharides or LPS) during puberty—a critical period for breast development—caused lasting inflammation and changes in gene expression that increased breast cancer risk later in life. Researchers discovered that a prebiotic supplement derived from shiitake mushrooms (AHCC) could counteract these harmful effects by reducing inflammation, regulating immune signaling molecules, and blocking cancer-promoting gene activity in mammary tissue. The findings suggest that gut health and inflammation during puberty may influence long-term breast cancer risk, and that dietary interventions like prebiotics might offer a preventive strategy, though human studies are needed to confirm these results.
2024
J Clin Oncol
The aim of this pooled analysis (taking data from 19 cohort studies from around the world) was to determine the effect (if any) of leisure-time physical activity on the premenopausal risk of breast cancer. Leisure time physical activity is defind as physical activity occuring during free time (so, not related to work). This analysis took data from a little over half a million women, where the incidence of breast cancer was about 10,000 across the studies. Hazard ratios (how often breast cancer occured in groups w/ high activity versus low activity) was used to asses relative risk. High levels of leisure time activity were associated with an approximately 10% reduction in breast cancer risk after adjusting for BMI. This association was found to be particuarily strong for human epidermal growth factor receptor 2–enriched breast cancer, with a 16-61% reduction in risk.
2024
Heliyon
A mouse study found that ginger volatile oil (GVO) reduced triple-negative breast cancer tumor growth in animals exposed to bisphenol A (BPA), a common plastic chemical known to promote cancer, with the effect linked to restoration of healthy gut bacteria. BPA exposure disrupted the gut microbiome by reducing bacterial diversity and beneficial bacteria like Lactobacillus, but treatment with ginger oil reversed these changes and increased the ratio of beneficial bacteria while decreasing harmful bacteria. The findings suggest that ginger compounds may counteract BPA’s cancer-promoting effects through their impact on the gut microbiome, offering a potential dietary strategy to mitigate harm from plastic chemical exposure, though human studies are needed to confirm these results.
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
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
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
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
Crit Rev Toxicol
A meta-analysis of 13 observational studies through May 2022 examined the dose-response relationship between per- and polyfluoroalkyl substances (PFAS) exposure—including PFOS, PFOA, PFNA, PFDA, and PFHxS—and risk of breast, prostate, colorectal, and ovarian cancers. The highest versus lowest exposure analysis found no significant associations between any PFAS compound and breast cancer (ORs ranging from 0.88-1.29), ovarian cancer (OR = 1.43), prostate cancer (OR = 1.05), or colorectal cancer (OR = 0.77). However, linear dose-response analysis revealed unexpected inverse associations, with each 1 ng/ml increase in PFNA and 2 ng/ml increase in PFOA associated with significant decreases in breast cancer risk (RR = 0.67 and 0.94, respectively), though non-linear analysis found no significant changes. The findings provide no evidence that PFAS exposure increases cancer risk for these sites, and the unexpected inverse associations observed in linear dose-response analyses—suggesting potential protective effects—are unexplained and may reflect study artifacts, reverse causation, or confounding factors rather than true biological protection, warranting further investigation to clarify these paradoxical relationships and determine whether they reflect real phenomena or methodological limitations.
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
Breast Cancer Res Treat
A large prospective study of 187,278 nurses followed for up to 31 years found that high levels of recreational physical activity (≥27 vs <3 MET-hours/week, roughly equivalent to ≥9 hours/week of brisk walking) were associated with 17% reduced breast cancer risk in both premenopausal and postmenopausal women. The protective effect was strongest for hormone receptor-positive (ER+/PR+) tumors in both groups, with no significant associations observed for hormone receptor-negative cancers, and while the benefit in postmenopausal women was partly explained by lower body weight, the association in premenopausal women remained independent of BMI. These findings provide strong evidence that regular recreational physical activity is a modifiable risk factor that reduces breast cancer risk across the lifespan, regardless of menopausal status, supporting public health recommendations for regular exercise as an accessible breast cancer prevention strategy for all women.
2024
Breast Cancer Res
A meta-analysis combining data from three cohort studies and one case-control study (3,793 estrogen receptor positive [ER+] and 627 ER- breast cancer cases) examined whether stopping alcohol consumption affects breast cancer risk by hormone receptor subtype. The study found that women who stopped drinking alcohol had a 12% lower risk of developing ER+ breast cancer compared to those who continued drinking (RR = 0.88), but cessation was not associated with reduced risk of ER- breast cancer (RR = 1.23). These findings suggest that quitting alcohol may reduce the risk of ER+ breast cancer specifically, which is noteworthy given that alcohol is an established risk factor for breast cancer, particularly hormone-receptor positive subtypes. The authors note that further research examining how long women have abstained from alcohol is needed to better understand the relationship between cessation duration and breast cancer risk.
2024
Cancer Epidemiol
A large collaborative study of 609,880 women from 16 prospective studies, including 9,956 breast cancer cases before age 55, examined when the relationship between body mass index (BMI) and breast cancer risk transitions from protective (before menopause) to harmful (after menopause). During the critical age window of 45-55 years, the study found that a five-unit BMI increment remained associated with reduced or neutral breast cancer risk across all menopausal status groups: HR=0.87 for premenopausal women, HR=1.00 for women after natural menopause, HR=0.99 after interventional loss of ovarian function, and HR=0.88 after hysterectomy without bilateral oophorectomy. The findings indicate that the well-documented reversal from BMI being protective to being a risk factor for breast cancer occurs after age 55, later than previously thought, suggesting that the transition to increased risk with higher BMI is not directly tied to the menopausal transition itself but occurs in the years following menopause. This timing provides important insight into how adiposity influences breast cancer risk across the lifespan and suggests that the hormonal and metabolic changes associated with higher BMI have different effects on breast tissue depending on age and years since menopause.
2024
Breast Cancer Res
A nested case-control study within the French E3N-Generations cohort examined 523 breast cancer cases and 523 matched controls to investigate whether thirteen metabolic health biomarkers mediate the relationship between exposure to three air pollutants (nitrogen dioxide, PCB153, and benzo[a]pyrene) and breast cancer risk. The study found that benzo[a]pyrene exposure was associated with a significant 2.32-fold increased breast cancer risk (highest vs. lowest quartile), PCB153 showed inconsistent positive associations, and nitrogen dioxide showed no association; among biomarkers, estradiol was associated with increased breast cancer risk (OR = 1.22 per SD). Four-way decomposition mediation analysis revealed suggestive evidence that albumin, HDL and LDL cholesterol, parathormone, and estradiol may partially mediate the associations between all three pollutants and breast cancer risk, though findings were limited by statistical power. These results provide preliminary mechanistic insights suggesting that air pollutants may influence breast cancer risk through alterations in metabolic biomarkers—particularly lipid metabolism and hormone regulation—though larger studies are needed to confirm these pathways and establish the clinical significance of these mediating effects in the relationship between environmental exposures and breast cancer development.
2024
Environ Int
A study in mice found that exposure to DEHP—a common chemical used to make plastics flexible—disrupts the gut-mammary connection, causing changes in gut bacteria, intestinal inflammation, and direct damage to mammary (breast) tissue that could impair milk production. DEHP altered gut microbiome composition (increasing some bacteria while decreasing others), changed blood metabolite levels, and its breakdown product (MEHP) triggered cell death in mammary tissue through multiple pathways. These findings raise concerns about DEHP exposure from plastics affecting both human breast health and dairy production in livestock, while identifying potential therapeutic targets to counteract the chemical’s harmful effects on the gut-breast axis.
2024
Maturitas
A prospective study of 24,892 Spanish women (639 breast cancer cases) from the EPIC cohort examined associations between three dietary patterns (Western, Prudent, Mediterranean) and breast cancer risk over time. Women with moderate-to-high adherence to the Western dietary pattern showed a non-linear 37% increased breast cancer risk compared to those with lowest adherence (HR = 1.37; 95% CI: 1.07-1.77 for third quartile and HR = 1.37; 95% CI: 1.03-1.83 for fourth quartile), with particularly strong associations in postmenopausal women (HR = 1.42; 95% CI: 1.04-1.94 in highest quartile) and for ER+/PR+/HER2- tumors (HR = 1.71; 95% CI: 1.11-2.63 in highest quartile), while Prudent and Mediterranean patterns showed no clear associations. The findings suggest that Western dietary patterns characterized by high-fat dairy, red and processed meats, refined grains, sweets, caloric drinks, and convenience foods may increase breast cancer risk, especially for hormone receptor-positive tumors in postmenopausal women.
2024
BMC Cancer
A case-control study of 133 breast cancer cases and 266 controls in Tehran, Iran used a food frequency questionnaire and the NOVA classification system to examine the association between processed foods (PFs) and ultra-processed foods (UPFs) consumption and breast cancer risk. In the initial model, women in the highest tertile of UPF consumption had nearly double the odds of breast cancer compared to the lowest tertile (OR = 1.93; 95% CI: 1.08-3.45), though this association was no longer significant after additional adjustments in a second model. However, when stratified by menopausal status, premenopausal women in the highest tertile of UPF consumption had more than 3.5 times higher odds of breast cancer (OR = 3.66; 95% CI: 1.33-10.08) in the fully adjusted model. These findings suggest that high consumption of ultra-processed foods may be particularly associated with increased breast cancer risk among premenopausal women, adding to the limited and sometimes contradictory evidence on the relationship between ultra-processed food intake and breast cancer.
2024
Ann Med
A study of 1,789 participants (including 263 breast cancer patients) from the National Health and Nutrition Examination Survey (NHANES) examined the associations between sleep duration, depression, and breast cancer risk, and developed machine learning algorithms to predict breast cancer. The study found that participants with depression had nearly double the odds of breast cancer (OR = 1.99; 95% CI: 1.55-3.51), while no significant association was observed between sleep duration (<7 hours, >9 hours compared to 7-9 hours) and breast cancer risk. Among six machine learning algorithms tested, the AdaBoost model performed best in predicting breast cancer with an area under the curve (AUC) of 0.84 (95% CI: 0.81-0.87), demonstrating good predictive capability. These findings suggest that depression, but not sleep duration, is significantly associated with increased breast cancer risk, providing new insights into the relationship between mental health and breast cancer while highlighting the need for further research into the underlying pathological mechanisms connecting depression and breast cancer development.