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2022
Ann Surg
A genomic study of 308 women with stage I-IV breast cancer (non-Hispanic White, Hispanic White, Hispanic Black, and non-Hispanic Black) using peripheral blood analysis found that increasing West African (WA) ancestry was associated with 6% higher odds of triple-negative breast cancer per percentage increase (OR = 1.06; 95% CI: 1.001-1.126) and higher neighborhood socioeconomic status (nSES) showed a protective effect (OR = 0.343; 95% CI: 0.151-0.781), though WA ancestry’s association with TNBC was attenuated when adjusting for nSES. Local ancestry analysis revealed nSES-independent enriched WA ancestral segments at specific chromosomal loci (χ²=42004914, p=3.70×10⁻⁵) associated with TNBC, while multinomial logistic regression demonstrated that women from low nSES neighborhoods remained more likely to have TNBC independent of genetic ancestry. These findings reveal the complex interplay between genetic ancestry and socioeconomic environment in TNBC etiology: while specific genetic variants linked to West African ancestry contribute to TNBC risk through biological mechanisms, neighborhood socioeconomic disadvantage exerts independent effects, highlighting that both genetic susceptibility and environmental/social determinants contribute to the disproportionate TNBC burden in Black women and underscoring the critical importance of studying gene-environment interactions as drivers of aggressive breast cancer disparities.
2022
Chemosphere
This case-control study found that higher urinary bisphenol A (BPA) levels were significantly associated with increased breast cancer (BC) risk, with a 54% higher risk per 1-unit increase in log-transformed BPA (95% CI: 1.34–1.77, P < 0.001). Additionally, genetic variation in the CYP17A1 gene (rs743572) significantly modified this association, with individuals carrying both high BPA levels and the GA+AA genotype showing a 2.49-fold increased BC risk (P interaction = 0.020).
2022
Cancer Epiemiol
The first Indian case-control study examining phthalates (chemicals widely used in plastics, cosmetics, and food packaging) and breast cancer found that women with higher urinary levels of di-butyl phthalate (DBP) had 1.5 times increased breast cancer risk, while those with higher DEHP levels had nearly 3 times increased risk. Analysis of breast tumor tissue revealed mutations in several genes known to respond to phthalate exposure, affecting pathways involved in hormones, metabolism, and cancer development. These findings suggest that exposure to certain phthalates may increase breast cancer risk through genetic changes, though larger studies are needed to confirm these results and understand how early-life exposures might contribute to cancer development later in life.
2022
Chemosphere
Researchers measured 41 endocrine-disrupting chemicals (EDCs) in women living in the Greater Manila Area, Philippines, comparing those with and without breast cancer. They found that certain perfluoroalkyl substances (PFAS) were significantly associated with breast cancer, with some chemicals showing dramatically increased risk: PFDoA was associated with a 1,263% increased risk, PFDA with an 826% increased risk, and PFHxA with a 166% increased risk. Long-chain PFAS levels were higher in women from heavily industrialized areas compared to the National Capital Region. This study provides the first baseline data on EDC exposure levels in Filipino women, filling a critical gap in knowledge about chemical exposures in Southeast Asian populations and suggesting that industrial pollution may be contributing to elevated PFAS levels and breast cancer risk.
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
Environ Int
A large French study of nearly 68,000 women followed for over 21 years found that dietary exposure to PBDEs (flame retardant chemicals) was associated with increased breast cancer risk, but importantly, this association was modified by vegetable oil consumption. Women who consumed higher amounts of vegetable oil (≥4.6 g/day) and had the highest PBDE intake showed a 23% increased breast cancer risk, while those with low vegetable oil consumption showed no increased risk regardless of PBDE exposure. These findings suggest that the interaction between diet and chemical contaminants is important to consider when developing public health recommendations, as certain dietary patterns may amplify or mitigate the health risks associated with environmental chemical exposures.
2022
Cancer Epidemiol Biomarkers Prev
A prospective Italian study of 496 breast cancer cases and matched controls found that women with the highest copper-to-zinc (Cu/Zn) ratio in their blood plasma had a 75% increased risk of developing breast cancer compared to those with the lowest ratio. Women with high Cu/Zn ratios in both plasma and urine showed an even more striking 137% increased risk. The association was particularly strong for cancers diagnosed within two years of measurement, suggesting that disrupted copper-zinc balance may serve as both an early marker of breast cancer and a potential risk factor, possibly opening avenues for preventive interventions targeting women with abnormal Cu/Zn homeostasis.
2022
Environ Int
A study of 48,450 women followed for over 10 years found that higher residential UV radiation exposure was associated with a 27% reduced risk of estrogen receptor-negative (ER-) breast cancer, but showed no association with overall breast cancer risk or ER-positive breast cancer. The protective effect against ER- breast cancer was particularly strong (48% risk reduction) among women who did not regularly take Vitamin D supplements, while those taking supplements showed no benefit from UV exposure. These findings suggest that UV-induced Vitamin D production may specifically protect against ER- breast cancer, a particularly aggressive subtype, supporting the importance of adequate Vitamin D levels through natural sunlight exposure or supplementation.
2022
Am J Clin Nutr
A large French study following over 80,000 women for nearly 9 years found that higher dietary acrylamide intake—a probable carcinogen formed when starchy foods like coffee, French fries, chips, and baked goods are cooked at high temperatures—was associated with a 40% increased risk of premenopausal breast cancer. The association showed a nonlinear pattern, with elevated risk at both moderate and high exposure levels, and was specifically linked to estrogen receptor-positive breast cancer, while no association was found for postmenopausal breast cancer. These findings support the need for continued efforts to reduce acrylamide formation in foods through improved cooking and processing methods, as dietary acrylamide exposure—averaging about 30 micrograms per day in this population—may be a modifiable risk factor for breast cancer, particularly in younger women.
2022
Environ Health
This large Chinese case-control study of 373 breast cancer patients and 657 controls found that higher plasma levels of PFOA and PFDA were positively associated with breast cancer risk, with PFOA showing particularly strong associations with hormone receptor-positive and HER2-positive breast cancers (47%, 36%, and 62% increased odds, respectively). Interestingly, the study found that PFTrDA (a longer-chain PFAS) was inversely associated with breast cancer risk, though the reasons for this protective effect are unclear. The findings add to growing international evidence linking PFAS exposure to breast cancer, demonstrating that these “forever chemicals” pose breast cancer risks not just in Europe and America but also in Asian populations. These results are concerning because PFOS was found at the highest concentrations in blood samples from both cases and controls, indicating widespread population exposure to these persistent environmental contaminants in Chin
2022
Environ Pollut
This Chinese prospective study of over 1,200 women found that higher baseline plasma concentrations of PFOA and PFHpA (a shorter-chain PFAS) were associated with 35% and 20% increased risk of developing breast cancer, respectively, with similar or stronger associations seen in postmenopausal women. When researchers examined the combined effect of all perfluorinated carboxylic acids together, they found a 19% increased breast cancer risk for each quartile increase in exposure, with PFOA accounting for more than half of this effect. Importantly, this is the first study to identify PFHpA—a shorter-chain PFAS increasingly used as a replacement for longer-chain compounds—as a breast cancer risk factor, raising concerns that newer “replacement” PFAS chemicals may not be safer alternatives. These prospective findings strengthen the evidence that PFAS exposure is a modifiable risk factor for breast cancer and support the need to regulate PFAS as an entire chemical class rather than individual compounds.
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.
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 Res
A study of 6,247 greenspace workers (landscapers, gardeners, groundskeepers) from the French AGRICAN cohort found significantly elevated cancer risks compared to farmers and non-agricultural workers. Male greenspace workers showed 15% higher overall cancer incidence, with particularly elevated risks for prostate cancer (21% increase), thyroid cancer (184% increase), testicular cancer (298% increase), and skin melanoma (115% increase), while female greenspace workers had a 71% increased risk of breast cancer. The study also found that greenspace workers reported more allergic diseases and, among males, more depression compared to other occupational groups. These findings highlight that greenspace workers face distinct occupational health risks, likely related to pesticide exposure and other workplace hazards, and should be studied separately from agricultural workers rather than being grouped together in research.
2021
Cancer Epi
This study of nearly 48,000 women found that frequent use of chemical hair straighteners and perms during adolescence (ages 10-13) was associated with more than double the risk of premenopausal breast cancer, though no increased risk was seen for postmenopausal breast cancer. Black women who used permanent hair dye during adolescence had a 77% increased breast cancer risk, though permanent dye use was uncommon overall in the study population. The findings are particularly concerning because adolescence is a critical developmental window when breast tissue may be more vulnerable to chemical exposures, and these hair products contain hormonally active and potentially carcinogenic compounds that may have long-lasting effects on breast cancer risk decades later.
2021
Int Arch Occup Environ Health
This case–control study in Northern Mexican women (394 breast cancer cases, 404 matched controls) measured urinary free-BPA (BPA‑F) and found that the highest exposure group had a statistically significant 2.31‑fold increased odds of breast cancer (95% CI: 1.43–3.74) compared to the lowest group. The authors concluded that BPA‑F may act as an environmental cofactor in breast carcinogenesis, although findings need replication.
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.
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
Environ Res
A French study of over 10,000 women found that long-term atmospheric exposure to PCB153, a widespread environmental pollutant with estrogen-like properties, was associated with a 19% increased risk of breast cancer for each standard deviation increase in cumulative exposure. The association was particularly strong for women who became postmenopausal during the study period (23% increased risk) and for estrogen receptor-positive breast cancers (18% increased risk), while no association was found for estrogen receptor-negative tumors. This is the first study to link airborne PCB exposure to breast cancer risk, providing evidence that these persistent environmental pollutants may contribute to hormone-sensitive breast cancer development even decades after their use was banned.
2021
Environ Int
Long-term exposure to benzo[a]pyrene (BaP), a toxic air pollutant from gas and diesel vehicle exhaust, was associated with a 15% increased risk of breast cancer in a large French study of over 10,000 women. The risk was particularly elevated in women transitioning through menopause and for hormone receptor-positive breast cancers, with each increase in BaP exposure levels raising breast cancer odds by 15-20%. This study provides important real-world evidence that BaP air pollution may contribute to breast cancer development, especially affecting hormone-sensitive tumors.
2021
Epidemiol
A study of 1,407 North Carolina women examined the relationship between blood levels of polychlorinated biphenyls (PCBs)—banned industrial chemicals that persist in the environment—and breast cancer risk. The researchers found that exposure to mixtures of PCBs was associated with increased breast cancer risk, with stronger associations observed among Black women (50% increased risk) compared to White women (10% increased risk) at higher exposure levels. Several individual PCB compounds showed elevated breast cancer risk when comparing highest to lowest exposure groups, with risk increases ranging from 20-40%. These findings support the hypothesis that PCB exposure may increase breast cancer risk, though additional studies in other populations are needed to confirm the results.
2021
Int J Clin Pract
A case-control study of 250 breast cancer patients and 250 controls found that women consuming diets that trigger higher insulin responses after meals—measured by dietary insulin index (DII) and dietary insulin load (DIL)—had 46-87% increased odds of breast cancer compared to those with lower scores. These high insulin-stimulating diets were more common among overweight women and those with family histories of cancer, suggesting that dietary patterns affecting blood insulin levels may be a modifiable risk factor for breast cancer. The findings support reducing consumption of foods that spike insulin levels—typically refined carbohydrates and high-glycemic foods—as a potential dietary strategy for breast cancer prevention, particularly for women at higher risk.
2021
Cancer Epidemiol Biomarkers Prev
A Spanish case-control study of 1,738 breast cancer cases and 1,910 controls found that occupational heat exposure was associated with a 22% increased risk of breast cancer among women who had ever been exposed. The study found significant dose-response relationships, with risk increasing with both cumulative heat exposure and duration of exposure, and particularly strong associations for hormone receptor-positive breast cancer (38% increased risk). The associations were strongest when not adjusted for detergent exposure, suggesting potential confounding or interaction between these workplace exposures. These findings suggest that chronic workplace heat stress may be a previously underrecognized occupational risk factor for breast cancer, though further research is needed to confirm these results and understand potential interactions with other workplace exposures.
2021
Environ Pollut
A pilot study of 250 predominantly postmenopausal women in Hawaii found that higher levels of AMPA (the primary breakdown product of the herbicide Glyphosate) in urine were associated with significantly increased breast cancer risk, with women in the highest exposure group having 4.5 times the risk compared to those with the lowest exposure. AMPA was detected in the urine of 90% of breast cancer cases and 84% of healthy controls, with cases showing 38% higher average AMPA levels. This is the first study to prospectively examine the link between AMPA exposure and breast cancer, and while the findings suggest a concerning association, the authors emphasize that larger studies are needed to confirm these preliminary results and explore potential differences across racial and ethnic groups.
2021
Environ Res
A nationwide Danish study of 1.8 million women followed from 2000-2017 found that each 10-decibel increase in 10-year average road traffic Noise exposure was associated with a 3.2% increased risk of breast cancer at the least exposed façade (typically bedrooms) and a very slight increased risk at the most exposed façade. Railway Noise showed similar patterns. The associations were strongest for HER2-negative breast cancer and suggest that nighttime Noise exposure during sleep may be particularly important, adding transportation Noise to the growing list of environmental breast cancer risk factors.
2021
Environ Res
This large U.S. study using NHANES data found that multiple PFAS chemicals were associated with increased odds of both breast and ovarian cancer, with dose-response relationships showing dramatically higher risks at the highest exposure levels—women in the highest quartile of exposure had 130% increased odds for breast cancer (up to 607% for PFHxS) and 77-125% increased odds for ovarian cancer compared to those in the lowest quartile. Different PFAS chemicals showed stronger correlations with different cancers: PFOA was most strongly correlated with breast cancer while PFHxS was most strongly correlated with ovarian cancer, suggesting these endocrine-disrupting chemicals may affect different hormone-sensitive tissues through distinct mechanisms. No associations were found with prostate or uterine cancers. These findings are particularly concerning because PFAS are ubiquitous environmental contaminants found in everyday products and the water supply, and the strong dose-response relationships suggest that reducing PFAS exposure could potentially lower the risk of these estrogen-related cancers in women.
2021
Scand J Work Environ Health
This large Danish study of over 38,000 women with breast cancer found that occupational exposure to diesel exhaust was associated with a modestly increased risk of estrogen receptor-negative breast tumors in women under age 50, with the risk increasing with longer duration and higher levels of exposure. No significant associations were found for overall breast cancer risk or for exposure to polycyclic aromatic hydrocarbons (PAHs). These findings suggest that workplace diesel exhaust exposure may be particularly relevant for early-onset, harder-to-treat forms of breast cancer, highlighting the importance of protecting workers from diesel fumes.
2021
Sci Total Environ
This Japanese case-control study of 405 matched pairs of women found that higher serum concentrations of PFAS chemicals were generally associated with reduced breast cancer risk rather than increased risk, with women in the highest exposure quartile showing 79-85% lower odds of breast cancer for linear isomers of PFOS and PFOA. However, the study revealed important differences between chemical structures: among postmenopausal women, while the linear form of one PFAS (PFTrDA) was protective, the branched form showed a marginally increased risk (74% higher odds approaching significance at medium exposure levels). These unexpected inverse associations contrast with several other studies showing increased breast cancer risk from PFAS exposure, highlighting the complexity of PFAS research and the importance of distinguishing between different chemical structures (branched vs. linear isomers) that may have opposite health effects, though the reasons for these protective associations remain unclear and warrant further investigation.
2021
Int J Epidemiol
This French study of over 13,000 postmenopausal women found that those with low dietary exposure to synthetic pesticides (primarily from eating organic foods) had a 43% lower breast cancer risk, while overweight and obese women with high exposure to certain pesticides (including chlorpyrifos and malathion) had over four times the breast cancer risk. The researchers estimated pesticide exposure by tracking whether participants ate conventional or organic versions of various foods and using a database of pesticide residues found on different crops. These findings suggest that dietary pesticide exposure from conventional foods may increase breast cancer risk, particularly in women who are overweight or obese, though more research is needed to confirm these results and understand the underlying mechanisms.
2021
Int J Cancer
In a nested case-control study of over 1,000 breast cancer cases and matched controls from the Multiethnic Cohort, pre-diagnostic urinary concentrations of bisphenol A (BPA), triclosan, and parabens were evaluated in relation to breast cancer risk. BPA was not significantly associated with risk; the highest tertile of total parabens had OR ≈ 0.77 (95% CI: 0.62–0.97) relative to the lowest tertile, indicating a modest inverse association. These results suggest that the relationships between common endocrine-disrupting chemicals and breast cancer may be more complex than anticipated and vary by exposure type.
Chronic long-term exposure to cadmium air pollution and breast cancer risk in the French E3N cohort.
2020
Cancer Epiemiol
A French study of over 8,000 women found no overall association between long-term airborne cadmium exposure and breast cancer risk, but unexpectedly discovered that higher cadmium exposure was associated with a 32-38% decreased risk of estrogen receptor-negative (ER-) breast cancers. This finding contradicts the hypothesis that cadmium increases breast cancer risk through its estrogen-like effects, and instead suggests cadmium may have different biological effects depending on the hormone receptor status of tumors. These surprising results indicate that cadmium’s relationship with breast cancer is more complex than previously thought and may involve mechanisms beyond its known estrogen-mimicking properties, requiring further research to understand why it might protect against hormone receptor-negative tumors.
2020
Environ Toxicol Pharmacol
This analysis of US health data from 2003-2012 found that women with higher long-term exposure to organophosphorus insecticides (common pesticides measured through urine samples) faced significantly elevated health risks, including three times higher risk of cardiovascular disease and 2.7 times higher overall cancer risk among women aged 60-85. Women with higher pesticide exposure also showed increased risks of asthma in younger age groups and chronic bronchitis in older age, with breast cancer risk elevated among female smokers and prostate cancer risk elevated among male smokers. These findings suggest that chronic exposure to these widely-used agricultural pesticides may pose greater health threats to women than men, particularly for cardiovascular disease and cancer.
2020
Int J Epidemiol
This Russian study of 468 breast cancer cases found that women exposed to prolonged low-level radiation from the Chernobyl nuclear accident had approximately three times higher breast cancer risk in the highest exposure groups compared to those with the lowest exposure, even though radiation doses were relatively low (averaging just 1.3 centigray). The study tracked women for about 25 years after the 1986 Chernobyl accident and estimated their radiation exposure based on where they lived and what they ate during that time. The findings suggest that even prolonged exposure to low levels of radiation—not just high-dose exposures—can increase breast cancer risk, particularly among women who were younger at the time of exposure.
2020
Int Arch Occup Environ Health
This Swedish study of 2,400 postmenopausal women found that those exposed to chemicals in the workplace had a 59% increased risk of breast cancer, with the risk increasing with longer duration of exposure. Women exposed to chlorinated hydrocarbon solvents or oil mist for more than 10 years had approximately triple the breast cancer risk compared to unexposed women. The study used individualized exposure assessments based on specific work tasks rather than just job titles, providing stronger evidence that workplace chemical exposures—particularly to organic solvents and oil mist commonly found in manufacturing and industrial settings—may be important contributors to breast cancer risk.
2020
JAMA
This long-term follow-up study of over 27,000 postmenopausal women in the Women’s Health Initiative tracked breast cancer outcomes for more than 20 years after participants were randomized to receive either hormone therapy or placebo. The results showed strikingly different effects depending on the type of hormone therapy: estrogen alone (CEE) in women who had undergone hysterectomy was associated with 22% lower breast cancer incidence and 40% lower breast cancer mortality, while estrogen plus progestin (CEE plus MPA) in women with an intact uterus was associated with 28% higher breast cancer incidence but no significant difference in breast cancer mortality. These findings indicate that the addition of progestin to estrogen therapy substantially changes its impact on breast cancer risk, with estrogen-alone therapy appearing protective and estrogen-plus-progestin therapy increasing risk. The study helps resolve longstanding uncertainty about menopausal hormone therapy and breast cancer by demonstrating that the type of hormone therapy and whether a woman has had a hysterectomy are critical factors in determining breast cancer outcomes.
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.
2020
Cancer Epidemiol
A study of 186,981 postmenopausal women in the NIH-AARP Diet and Health Study found that those living in areas with the highest levels of outdoor light at night (LAN) had a 10% increased risk of developing breast cancer over 16 years of follow-up compared to women in the darkest areas. The association was stronger for estrogen receptor-positive breast cancer (12% increased risk) and appeared to vary by individual characteristics such as smoking, alcohol consumption, sleep duration, and body mass index. These findings suggest that nighttime light pollution may disrupt circadian rhythms and contribute to breast cancer development, particularly hormone-sensitive tumors. The results highlight artificial light at night as a potentially modifiable environmental risk factor for postmenopausal breast cancer, with implications for urban planning and outdoor lighting policies.
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
Br Med J
A large UK study of 98,611 women with breast cancer and 457,498 controls found that long-term hormone replacement therapy (HRT) use (≥5 years) was associated with significantly increased breast cancer risk, with combined estrogen-progestogen therapy showing a 79% increased risk and estrogen-only therapy showing a 15% increased risk. Among combined therapies, norethisterone carried the highest risk (88% increase) while dydrogesterone showed the lowest (24% increase), and importantly, the increased risk from past long-term combined therapy use persisted even after stopping treatment (16% increased risk). In practical terms, recent combined HRT users could expect 9-36 extra breast cancer cases per 10,000 women per year depending on age, while estrogen-only users would see 3-8 extra cases per 10,000 women per year, providing critical information for women and clinicians weighing the benefits and risks of different HRT regimens.
2020
Breast Cancer Res
A study of 118,760 postmenopausal women in the NIH-AARP cohort found that combined estrogen-progestogen therapy (EPT) was associated with a 54% increased breast cancer risk overall, with risk doubling for women using EPT for 10 or more years and reaching an 80% increased risk for those who continued use through 2004. Importantly, women who discontinued EPT showed no increased risk (14% non-significant increase), suggesting the elevated risk may be reversible after stopping treatment. Estrogen-only therapy (ET) showed no increased risk at baseline, though a 35% increased risk emerged in women who continued use through 2004, and EPT was associated with elevated risk across all breast cancer subtypes including in situ disease, invasive cancers, and tumors of varying hormone receptor status.
2020
Environ Int
This Taiwanese study of 239 women found that higher plasma levels of PFOS (a “forever chemical”) were associated with 134% increased breast cancer risk in women aged 50 and younger, with each natural log unit increase in exposure more than doubling the odds of developing the disease. Both PFOS and PFHxS (another PFAS chemical) showed positive associations specifically with estrogen receptor-positive breast tumors in younger women, suggesting these endocrine-disrupting chemicals may particularly affect hormone-sensitive breast cancers during reproductive years. These findings are concerning because PFAS are ubiquitous environmental contaminants found in water, food packaging, and consumer products, and the study adds to growing evidence that these persistent chemicals may contribute to rising breast cancer rates among younger women. The results highlight the potential health consequences of widespread PFAS contamination, particularly for women of reproductive age who may face elevated risk of hormone-driven breast cancers.
2020
Int J Cancer
his French study of 388 women found that higher blood levels of PFOS (a “forever chemical”) were associated with 122-133% increased breast cancer risk for estrogen receptor-positive tumors and 147-176% increased risk for progesterone receptor-positive tumors, with a clear dose-response relationship showing increasing risk at higher exposure levels. Interestingly, the study found different patterns for hormone receptor-negative tumors, where only low-to-moderate levels of PFOS and PFOA were associated with dramatically increased risk (up to 1,440% for estrogen receptor-negative tumors at moderate PFOS levels). These findings suggest that PFAS chemicals—which are widespread in human blood worldwide due to contamination from products like stain-resistant fabrics, non-stick cookware, and food packaging—may contribute to breast cancer through different mechanisms depending on tumor type, highlighting the complexity of how these persistent environmental chemicals affect breast cancer risk.
2020
Basic Clin Pharmacol Toxicol
This case-control study of serum-levels of persistent organic pollutants among Greenlandic Inuit included 74 breast cancer cases and 80 matched controls. Researchers measured blood methylation of repetitive elements (LINE-1) and genes such as ATM and ESR2, alongside serum persistent organic pollutant (POP) levels. They found that women in the second tertile of ATM methylation had OR ≈ 2.33 (95% CI: 1.04–5.23) and those in the third tertile of ESR2 methylation had OR = 2.22 (95% CI: 0.97–5.05); women in the highest tertile of LINE-1 methylation had OR = 0.42 (95% CI: 0.18–0.98). These results suggest that altered DNA methylation associated with environmental pollutant burdens may play a role in breast cancer etiology in this population.
2019
J Natl Cancer Inst
This study of over 700 women found that DDT exposure was associated with increased breast cancer risk through age 54, but the timing of first exposure mattered critically: women first exposed to DDT after infancy had nearly triple the risk of early postmenopausal breast cancer (ages 50-54), while women first exposed during infancy through puberty had nearly four times the risk of premenopausal breast cancer (before age 50). These findings suggest there are specific windows of vulnerability when DDT exposure has the strongest impact on future breast cancer risk, with effects that can persist for decades. The results support the idea that DDT acts as an endocrine disruptor affecting breast tissue throughout a woman’s life—from before birth through menopause—even though DDT was banned in the U.S. in 1972, highlighting the long-term health consequences of early-life chemical exposures.
2019
Int J Env Res Pub Health
This Brazilian case-control study of 351 women in an intensive agricultural region found that women living near cropland where pesticides are used had more than twice the risk of developing breast cancer compared to those who didn’t live near such areas. The study also found that women over 50 who experienced early menarche (first menstrual period at 9-12 years) had approximately double the breast cancer risk. These findings suggest that residential proximity to pesticide-treated agricultural land may be an important environmental risk factor for breast cancer, adding to concerns about pesticide exposure beyond just occupational settings or dietary intake.
2019
Epidemiol
A large US study of nearly 51,000 women found that exposure to airborne toxic metals, particularly mercury, cadmium, and lead, was associated with increased postmenopausal breast cancer risk, with mercury showing the strongest effect at 30% increased risk for the highest exposure levels. When examining the combined effect of 10 different airborne metals together, the mixture was associated with elevated postmenopausal breast cancer risk, with mercury, lead, and cadmium contributing most to this increased risk. These findings suggest that environmental exposure to toxic metals through air pollution may be an important and underrecognized risk factor specifically for breast cancer in postmenopausal women.
2019
J Clin Oncl
This large-scale Danish nationwide study followed 1.12 million women over nearly 10 million woman-years to examine the relationship between phthalate exposure from prescription medications and breast cancer risk. The researchers tracked phthalate exposure by linking a database of drug ingredients with prescription records, finding that most phthalate exposures were not associated with increased breast cancer risk. However, high-level cumulative exposure to dibutyl phthalate (≥10,000 mg) was associated with approximately double the risk of estrogen receptor-positive breast cancer, consistent with laboratory evidence showing this compound has estrogenic effects. The study concludes that women should avoid high-level dibutyl phthalate exposure, particularly through long-term use of pharmaceuticals containing this compound, though lower exposure levels did not increase breast cancer risk.
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
Environ Int
This population-based case-control study investigated whether occupational exposure to alkylphenolic compounds—endocrine-disrupting chemicals widely used in industry—is associated with breast and prostate cancer. The study included over 5,600 participants and found that occupational exposure to alkylphenolic compounds was modestly associated with increased breast cancer risk (23% increase), particularly from exposure to domestic cleaning products and nonylphenol ethoxylates. No significant associations were found between alkylphenolic compound exposure and prostate cancer overall, except among men exposed through cosmetics and personal hygiene products. The authors conclude these findings suggest a modest link between occupational alkylphenolic compound exposure and breast cancer that requires further confirmation in additional studies.