Causes and Risk Factors of Breast Cancer, What Do We Know for Sure? An Evidence Synthesis of Systematic Reviews and Meta-Analyses

Breast cancer affected more than 2.3 million women in 2022 and is the most diagnosed cancer among women worldwide. The incidence rates are greater in developed regions and are significantly higher among women with higher education and socioeconomic status. Therefore, it is reasonable to assume that the way women live their lives may impact their risk of being diagnosed with breast cancer. This systematic review aimed to identify what is known about the causes and risk factors of breast cancer, excluding genetic causes. A comprehensive systematic search identified 2387 systematic reviews, 122 were included and six overall themes identified. In our "top list" with the 36 most important findings, a study of breast density had the highest effect size for increasing the risk of breast cancer, and a high sex-hormone-binding globulin level was the most protective factor. Many of the included studies investigating the same topics had conflicting results. The conclusion from this evidence synthesis reveals a lack of consensus of factors associated with the causes and risk of breast cancer. These findings suggest that recommendations about lifestyle and breast cancer should be made with caution.

Breast Cancer and Lifestyle Factors: Umbrella Review

Lifestyle factors play a major role in the risk of breast cancer. This review aimed to examine the size of the effect of select lifestyle factors on risk for breast cancer and assess the quality of existing evidence. The authors performed an umbrella review of systematic reviews. The authors found an increased risk for breast cancer associated with obesity, alcohol intake, and smoking and a decreased risk due to physical activity. The evidence for sleep disruption and duration indicates risk for breast cancer, but it is limited in size, statistical significance, and quality of evidence.

Determinants of breast cancer in Ethiopia: a systematic review and meta-analysis

Background

Breast cancer (BC) is the first leading cancer sharing about 25% of the cancer burden among women globally. This study aimed to identify the determinants of BC in Ethiopia.

Methods

We comprehensively searched primary studies conducted in Ethiopia on associated factors of BC in PubMed, Cochrane Library, Hinari, Google, and Google Scholar) and available online until 2 June 2023. The necessary data were extracted from relevant studies and exported to STATA version 15 for analysis. The pooled odds ratio with its 95% confidence interval (CI) was estimated using a random effect model. The finding was reported following preferred reporting items for systematic reviews and meta-analyses guidelines.

Results

Five studies with 1,819 participants (792 cases and 1,027 controls) were included. The significant determinants of BC were age at menarche <12 years (adjusted odds ratio (AOR) = 3.36, 95% CI: 1.68-5.04), post-menopause (AOR = 2.37, 95% CI: 1.67-3.06), ever breastfeeding (AOR = 0.28, 95% CI: 0.15-0.42), and family history of cancer (AOR = 2.39, 95% CI: 1.29-3.44).

Conclusion

In Ethiopia, the significant determinants of BC among women were age at menarche <12 years, post-menopause, Ever breastfeeding, and family history of cancer. We recommend that the concerned organizations consider the aforementioned factors in addressing the problem of BC in Ethiopia by increasing community awareness, promoting breast self-examination, and developing programs to reduce the increasing burden of BC in the study setting.

Factors for the Primary Prevention of Breast Cancer: A Meta-Analysis of Prospective Cohort Studies

Background: This report provided the effect of 15 preventable factors on the risk of breast cancer incidence.

Study design: A systematic review and meta-analysis.

Methods: A detailed research was conducted on PubMed, Web of Science, and Scopus databases in January 2020. Reference lists were also screened. Prospective cohort studies addressing the associations between breast cancer and 15 factors were analyzed. Between-study heterogeneity was investigated using the χ², τ², and I² statistics. The probability of publication bias was explored using the Begg and Egger tests and trim-and-fill analysis. Effect sizes were expressed as risk ratios (RRs) with 95% confidence intervals (CIs) using a random-effects model.

Results: Based on the results, out of 147,083 identified studies, 197 were eligible, including 19,413,702 participants. The RRs (95% CI) of factors associated with breast cancer were as follows: cigarette smoking 1.07 (1.05, 1.09); alcohol drinking 1.10 (1.07, 1.12); sufficient physical activity 0.90 (0.86, 0.95); overweight/obesity in premenopausal 0.92 (0.82, 1.03) and postmenopausal 1.18 (1.13, 1.24); nulliparity 1.16 (1.03, 1.31); late pregnancy 1.37 (1.25, 1.50); breastfeeding 0.87 (0.81, 0.93); ever using oral contraceptive 1.00 (0.96, 1.05); ever using estrogen 1.13 (1.04, 1.23); ever using progesterone 1.02 (0.84, 1.24); ever using estrogen/progesterone 1.60 (1.42, 1.80); ever taking hormone replacement therapy 1.26 (1.20, 1.32); red meat consumption 1.05 (1.00, 1.11); fruit/vegetable consumption 0.87 (0.83, 0.90); and history of radiation therapy, based on single study 1.31 (0.87, 1.98).

Conclusions: This meta-analysis provided a clear picture of several factors associated with the development of breast cancer. Moreover, the useful information in this study may be utilized for ranking and prioritizing preventable risk factors to implement effective prevention programs.

Heterocyclic Aromatic Amines in Meat: Formation, Isolation, Risk Assessment, and Inhibitory Effect of Plant Extracts

Heterocyclic aromatic amines (HAAs) are potent carcinogenic compounds induced by the Maillard reaction in well-done cooked meats. Free amino acids, protein, creatinine, reducing sugars and nucleosides are major precursors involved in the production of polar and non-polar HAAs. The variety and yield of HAAs are linked with various factors such as meat type, heating time and temperature, cooking method and equipment, fresh meat storage time, raw material and additives, precursor’s presence, water activity, and pH level. For the isolation and identification of HAAs, advanced chromatography and spectroscopy techniques have been employed. These potent mutagens are the etiology of several types of human cancers at the ng/g level and are 100- to 2000-fold stronger than that of aflatoxins and benzopyrene, respectively. This review summarizes previous studies on the formation and types of potent mutagenic and/or carcinogenic HAAs in cooked meats. Furthermore, occurrence, risk assessment, and factors affecting HAA formation are discussed in detail. Additionally, sample extraction procedure and quantification techniques to determine these compounds are analyzed and described. Finally, an overview is presented on the promising strategy to mitigate the risk of HAAs by natural compounds and the effect of plant extracts containing antioxidants to reduce or inhibit the formation of these carcinogenic substances in cooked meats.

National and Subnational Incidence, Mortality, and Years of Life Lost Due to Breast Cancer in Iran: Trends and Age-Period-Cohort Analysis Since 1990

Breast cancer is the most common cancer among women, causing considerable burden and mortality. Demographic and lifestyle transitions in low and low-middle income countries have given rise to its increased incidence. The successful management of cancer relies on evidence-based policies taking into account national epidemiologic settings. We aimed to report the national and subnational trends of breast cancer incidence, mortality, years of life lost (YLL) and mortality to incidence ratio (MIR) since 1990. As part of the National and Subnational Burden of Diseases project, we estimated incidence, mortality and YLL of breast cancer by sex, age, province, and year using a two-stage spatio-temporal model, based on the primary dataset of national cancer and death registry. MIR was calculated as a quality of care indicator. Age-period-cohort analysis was used to distinguish the effects of these three collinear factors. A significant threefold increase in age-specific incidence at national and subnational levels along with a twofold extension of provincial disparity was observed. Although mortality has slightly decreased since 2000, a positive mortality annual percent change was detected in patients aged 25-34 years, leading to raised YLLs. A significant declining pattern of MIR and lower provincial MIR disparity was observed. We observed a secular increase of breast cancer incidence. Further evaluation of risk factors and developing national screening policies is recommended. A descending pattern of mortality, YLL and MIR at national and subnational levels reflects improved quality of care, even though mortality among younger age groups should be specifically addressed.

National and Subnational Incidence, Mortality, and Years of Life Lost Due to Breast Cancer in Iran: Trends and Age-Period-Cohort Analysis Since 1990

Breast cancer is the most common cancer among women, causing considerable burden and mortality. Demographic and lifestyle transitions in low and low-middle income countries have given rise to its increased incidence. The successful management of cancer relies on evidence-based policies taking into account national epidemiologic settings. We aimed to report the national and subnational trends of breast cancer incidence, mortality, years of life lost (YLL) and mortality to incidence ratio (MIR) since 1990. As part of the National and Subnational Burden of Diseases project, we estimated incidence, mortality and YLL of breast cancer by sex, age, province, and year using a two-stage spatio-temporal model, based on the primary dataset of national cancer and death registry. MIR was calculated as a quality of care indicator. Age-period-cohort analysis was used to distinguish the effects of these three collinear factors. A significant threefold increase in age-specific incidence at national and subnational levels along with a twofold extension of provincial disparity was observed. Although mortality has slightly decreased since 2000, a positive mortality annual percent change was detected in patients aged 25-34 years, leading to raised YLLs. A significant declining pattern of MIR and lower provincial MIR disparity was observed. We observed a secular increase of breast cancer incidence. Further evaluation of risk factors and developing national screening policies is recommended. A descending pattern of mortality, YLL and MIR at national and subnational levels reflects improved quality of care, even though mortality among younger age groups should be specifically addressed.

Heterocyclic aromatic amines in doner kebab: Quantitation using an efficient microextraction technique coupled with reversed-phase high-performance liquid chromatography

The safety of doner kebab as a traditional Middle East tasty food can threaten via the formation of dangerous compounds such as heterocyclic aromatic amines during heat process. In this regard, the current investigation was devoted to measuring of 4 HAAs (2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)) in doner kebab samples with an innovative microextraction technique combined with high-performance liquid chromatography. The limit of detection was in the range of 4.8 and 5.3 ng/g, while relative standard deviations were between 6.5% and 8.3%, and recoveries were calculated in the range of 89%-97%. The most and the least total mean values of HAA levels were 13.30 ng/g for MeIQx and 5.0 ng/g for IQ. The proposed method showed a high capability to extract trace amount of HAAs from a complex matrix such as doner kebab. Also, this technique is easy, high sensitive, selective, accurate and efficient.

Common risk factors for major noncommunicable disease, a systematic overview of reviews and commentary: the implied potential for targeted risk reduction

Noncommunicable disease now contributes to the World Health Organization top 10 causes of death in low-, middle- and high-income countries. Particular examples include stroke, coronary heart disease, dementia and certain cancers. Research linking clinical and lifestyle risk factors to increased risk of noncommunicable disease is now well established with examples of confirmed risk factors, including smoking, physical inactivity, obesity and hypertension. However, despite a need to target our resources to achieve risk reduction, relatively little work has examined the overlap between the risk factors for these main noncommunicable diseases. Our high-level review draws together the evidence in this area. Using a systematic overview of reviews, we demonstrate the likely commonality of established risk factors having an impact on multiple noncommunicable disease outcomes. For example, systematic reviews of the evidence on physical inactivity and poor diet found each to be associated with increased risk of cancers, coronary heart disease, stroke, diabetes mellitus and dementia. We highlight the potential for targeted risk reduction to simultaneously impact multiple noncommunicable disease areas. These relationships now need to be further quantified to allow the most effective development of public health interventions in this area.

Cancer Incidence in Kerman Province, Southeast of Iran: Report of an ongoing Population-Based Cancer Registry, 2014

Introduction: The epidemiology of common cancers in Kerman province, southeast of Iran, was assessed based upon results of the Kerman Population-Based Cancer Registry Program (KPBCR). Methods: in this retrospective study, all patients diagnosed with primary cancers and registered with the KPBCR were included. New cancer cases registered from 2014 were identified from pathological labs, medical reports of 48 health facilities providing cancer diagnosis or treatment services and the national death registry program. Data for patients who were referred to neighboring provinces to access health services were also collected from national referral registries. Results from autopsies was additionally extracted from regional forensic and legal medicine centers and added to the registry periodically. Age standardized incidence rates (ASRs) per 100,000 person-years for all cancers were computed, using direct-standardization and CanReg methodology. Mortality to incidence (M:I) ratios and microscopically verified (MV) proportions were calculated as quality measures. Results: A total of 2,838 cases of cancer were registered in Kerman province, 2014. Of these 45. 6% involved women (n=1,293). Individuals aged 60-64 years represented the largest proportion (11.6%) of the total cancer prevalence, followed by those aged 55-59 years (10.86%) and 65-69 years (8.99%). The ASRs for all cancers were 155.1 and 118.90 per 100,000, in men and women, respectively. In women, breast (ASR: 26.4), skin (ASR: 13.0), thyroid (ASR: 9.2), leukemia (ASR: 8.0) and colorectal (ASR: 7.70) were the most common cancers. In men, bladder (ASR: 24.70), skin (ASR: 16.80), lung (ASR: 14.6), leukemia (ASR: 14.50), and stomach (ASR: 10.8) were found to be the most frequent. Conclusion: This study provided latest evidence on epidemiology of cancer in the southeast of Iran that could be used to empower prevention and control interventions in a developing country.

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

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

A summary of meat intakes and health burdens

This review summarizes published meta-analysis outcomes on the associations between meat intakes and burden of diseases. A novel assessment process was developed, combining selected Cochrane Review measures, AMSTAR checklist, and other quality measures identified by authors during preliminary phases of the review process. Meat intakes have been found to be statistically significant associated with 21 burden of diseases. A total of 37 risk-outcome best dose-response estimations were identified, all were positively associated, and 21 of them with low to moderate, or insignificant heterogeneity. The highest dose-responses per 50 g increases in processed meat intake at 95% confident levels were 1.81 (1.32, 2.48) for esophageal cancer, 1.71 (1.34, 2.19) for stomach cancer, 1.42 (1.07, 1.89) for CHD, 1.32 (1.19, 1.48) for diabetes, and 1.24 (1.13, 1.35) for colon cancer incidences, and 1.24 (1.09, 1.40) for CVD mortality. The highest dose-responses per each 65 g increases in total red meat intake were 1.36 (1.16, 1.58) for endometrial cancer, 1.25 (1.10, 1.41) esophageal cancer, and 1.22 (1.16, 1.23) for lung cancer incidences. In addition, 14 statistically significant associations in terms of high vs low meat intake relative risks were also identified. Total red meat intakes were found negatively associated with CVD and cancer mortalities, and poultry meat intakes were found negatively associated with all-cause and cancer mortalities, and rectal cancer incidences in low meat consumption Asian countries. Current global and dietary Comparative Risk Assessments may underestimate burden of diseases attributed to meat intakes. More investigation is needed in low-meat consumption countries.

The Investigation of Risk Factors Impacting Breast Cancer in Guilan Province

Introduction:

Breast cancer is multifactorial therefore more recognition of risk factors is important in its prevention.

Objective:

This study was conducted in order to determine the factors influencing breast cancer in women referred to health centers in Guilan province in 2015-2016.

Method:

In a case- control study, 225 women with breast cancer were investigated. The control group consisted of 225 healthy women of the relatives (third-rank) whose phone numbers were obtained from the patients. Data were collected through telephone interviews.

Results:

The risk of breast cancer raised in women who have a family history of other cancers (OR= 3.5; 95% CI= 1.96-6.6), exposure to X-Ray (OR= 2.5; 95% CI=1.1-5.5), having more than 4 children (OR= 2.695% CI=1.2-4.8), age more than 36 years at first pregnancy(OR=2.3; 95% CI=0.7-5.1), primary levelof education (OR= 5.4;95% CI=2.8-11.2) and inadequate intake of fruit (OR=1.5; 95% CI=1-2.2). Also, presence of the following factors reduced breast cancer risk: regular menstruation (OR= 0.66; CI=0.4-0.9), duration of breastfeeding more than 12 months, less than 6 months and 7-12 months (OR=0.23; 95% CI=0.09-0.59, OR=0.29; 95% CI=0.17-0.49 and OR=0.03; 95% CI=0.01-0.08) and parity (OR=0.4; 95% CI=0.27-0.83) In multiple linear regression analysis of higher education (OR=0.16; 95% CI=0.03-0.77), using contraceptives for more than 16 years (OR=2.3; 95% CI=1.4-3.9), family history of other cancers (OR=6.1; 95% CI=1.9-19.3) and a history of X-Ray exposure (OR=4.4; 95% CI=1.07-18.1) were considered as predictive factors.

Conclusion:

The results of this study emphasize the importance of informing women about breast cancer risk factors. So, identification of these risk factors is required as important means of prevention and treatment of breast cancer.

Evaluation of Common Risk Factors for Breast Carcinoma in Females: a Hospital Based Study in Karachi, Pakistan

BACKGROUND

Breast malignancies are one of the leading causes of deaths in females worldwide. There are a number of risk factors associated with breast cancer but in Karachi Pakistan there are insufficient data available.

MATERIALS AND METHODS

A case control study was conducted on females in age group between 30-80 years. This study was accomplished by retrospective data collection in Aga Khan University Hospital Karachi, Pakistan. A total of 108 females with primary malignancy of breast were included along with 108 matched controls. Relationship of various factors with disease was studied using logistic regression to calculate odds ratios with 95 % confidence intervals.

RESULTS

A total of 14 variables were analyzed and based on and 7 were found to be risk factors: old age, family history of breast cancer, family history of other carcinomas, personal history of breast carcinoma, early age of menarche, older age of mother at first delivery and lower number of children. Five factors, parity, breast feeding, history of oral contraceptive pills intake, past history of oophorectomy and hysterectomy showed protective associations. One variable, use of hormonal replacement therapy, showed a controversial link and one other, marital status, was not significant in this study.

CONCLUSIONS

It is concluded that most of the well-known risk factors for breast cancer are also associated with the disease in the female population of Karachi, Pakistan. High risk patients should be the focus with the help of this study so that screening can be more effective for early diagnosis before clinically evident breast malignancy.

Associations of demographic and socioeconomic factors with stage at diagnosis of breast cancer

BACKGROUND

Stage at diagnosis is one of the most important prognostic factors of breast cancer survival. Because in the breast cancer case this may vary with socioeconomic characteristics, this study was performed to recognize the relationship between demographic and socioeconomic factors with stage at diagnosis in Iran.

MATERIALS AND METHODS

This cross-sectional, descriptive study conducted on 526 patients suffering from breast cancer and registered in Cancer Research Center of Shahid Beheshti University of Medical Sciences from 2008 to 2013. A reliable and valid questionnaire about family levels of socioeconomic status filled in by interviewing the patients via phone. For analyzing the data, Multinomial logistic regression, Kendal tau-b correlation coefficient and Contingency Coefficient tests were executed by SPSS22. Economic status, educational attainment of patient and household head and/or a combination of these were considered as parameters for socioeconomic status. First, the relationship between stage at diagnosis and demographic and socioeconomic status was assessed in univariate analysis then these relationships assessed in two different models of multinomial logistic regression.

RESULTS

The mean age of the patients was 48.3 (SD=11.4). According to the results of this study, there were significant relationships between stage at diagnosis of breast cancer with patient education (p=0.011), living place (p=0.044) and combined socioeconomic status (p=0.024). These relationships persisted in multiple multinomial logistic regressions. Other variables, however, had no significant correlation.

CONCLUSIONS

Patient education, combined socioeconomic status and living place are important variables in stage at diagnosis of breast cancer in Iranian women. Interventions have to be applied with the aim of raising women's accessibility to diagnostic and medical facilities and also awareness in order to reducing delay in referring. In addition, covering breast cancer screening services by insurance is recommended.

Meat consumption and cancer risk: a critical review of published meta-analyses

Dietary habits play a substantial role for increasing or reducing cancer risk. We performed a critical review of scientific literature, to describe the findings of meta-analyses that explored the association between meat consumption and cancer risk. Overall, 42 eligible meta-analyses were included in this review, in which meat consumption was assumed from sheer statistics. Convincing association was found between larger intake of red meat and cancer, especially with colorectal, lung, esophageal and gastric malignancies. Increased consumption of processed meat was also found to be associated with colorectal, esophageal, gastric and bladder cancers. Enhanced intake of white meat or poultry was found to be negatively associated with some types of cancers. Larger beef consumption was significantly associated with cancer, whereas the risk was not increased consuming high amounts of pork. Our analysis suggest increased risk of cancer in subjects consuming large amounts of red and processed meat, but not in those with high intake of white meat or poultry.

Prolonged use of human insulin increases breast cancer risk in Taiwanese women with type 2 diabetes

Background

Human insulin is commonly used to treat hyperglycemia in patients with diabetes, but its potential link with female breast cancer is under debate. This study investigated whether human insulin use might be associated with breast cancer risk in Taiwanese women with type 2 diabetes.

Methods

The reimbursement databases of all Taiwanese diabetic patients from 1996 to 2009 were retrieved from the National Health Insurance. An entry date was set at 1 January 2004 and a total of 482,033 women with type 2 diabetes were followed up for breast cancer incidence until the end of 2009. Incidences for ever-users, never-users and subgroups of human insulin exposure (using tertile cutoffs of time since starting insulin, cumulative dose and cumulative duration of insulin) were calculated and the adjusted hazard ratios were estimated by Cox regression. The potential risk modification by concomitant treatment with metformin, statin and angiotensin converting enzyme inhibitor/angiotensin receptor blocker (ACEI/ARB) was also evaluated.

Results

There were 59,798 ever-users and 422,235 never-users of human insulin, with respective numbers of incident breast cancer of 559 (0.93 %) and 4,711 (1.12 %), and respective incidence of 207.9 and 215.1 per 100,000 person-years. The overall adjusted hazard ratio (95 % confidence interval) did not show a significant association with insulin [1.033 (0.936-1.139)]. However, patients in the third tertiles of dose–response parameters might show a significantly higher risk of breast cancer while compared to never-users: 1.185 (1.026-1.368), 1.260 (1.096-1.450) and 1.257 (1.094-1.446) for ≥67 months for time since starting insulin, ≥39,000 units for cumulative dose of insulin, and ≥21.8 months for cumulative duration of insulin, respectively. Additional analyses suggested that the breast cancer risk associated with human insulin use might be beneficially modified by concomitant use of metformin, statin and ACEI/ARB.

Conclusions

This study discloses a significantly higher risk of breast cancer associated with prolonged use of human insulin. The increased risk of breast cancer associated with human insulin use may be modified by medications such as metformin, statin and ACEI/ARB.