Insulin-like growth factor 2 hypermethylation in peripheral blood leukocytes and colorectal cancer risk and prognosis: a propensity score analysis.

Background: To comprehensively assess and validate the associations between insulin-like growth factor 2 (IGF2) gene methylation in peripheral blood leukocytes (PBLs) and colorectal cancer (CRC) risk and prognosis. Methods: The association between IGF2 methylation in PBLs and CRC risk was initially evaluated in a case-control study and then validated in a nested case-control study and a twins' case-control study, respectively. Meanwhile, an initial CRC patient cohort was used to assess the effect of IGF2 methylation on CRC prognosis and then the finding was validated in the EPIC-Italy CRC cohort and TCGA datasets. A propensity score (PS) analysis was performed to control for confounders, and extensive sensitivity analyses were performed to assess the robustness of our findings. Results: PBL IGF2 hypermethylation was associated with an increased risk of CRC in the initial study (ORPS-adjusted, 2.57, 95% CI: 1.65 to 4.03, P<0.0001), and this association was validated using two independent external datasets (ORPS-adjusted, 2.21, 95% CI: 1.28 to 3.81, P=0.0042 and ORPS-adjusted, 10.65, 95% CI: 1.26 to 89.71, P=0.0295, respectively). CRC patients with IGF2 hypermethylation in PBLs had significantly improved overall survival compared to those patients with IGF2 hypomethylation (HRPS-adjusted, 0.47, 95% CI: 0.29 to 0.76, P=0.0019). The prognostic signature was also observed in the EPIC-Italy CRC cohort, although the HR did not reach statistical significance (HRPS-adjusted, 0.69, 95% CI: 0.37 to 1.27, P=0.2359). Conclusions: IGF2 hypermethylation may serve as a potential blood-based predictive biomarker for the identification of individuals at high risk of developing CRC and for CRC prognosis.

Association between the methylation of CpG islands in JAK-STAT pathway-related genes and colorectal cancer.

BACKGROUND: Aberrant promoter methylation of CpG islands plays an important role in carcinogenesis. However, the association between the DNA methylation of JAK-STAT pathway-related genes in peripheral blood leukocytes and colorectal cancer (CRC) susceptibility remains unclear. METHODS: We conducted a case-control study of 403 patients with CRC and 419 cancer free controls, and the DNA methylation levels of JAK2, STAT1, STAT3, and SOCS3 in peripheral blood samples from all subjects were assessed using a methylation-sensitive high-resolution melting (MS-HRM) analysis. RESULTS: Compared with controls, the methylation of the JAK2, STAT1 and SOCS3 genes increased the CRC risk (ORadjusted=1.96, 95% CI, 1.12-3.41, P=0.01; ORadjusted=5.37, 95% CI, 3.74-7.71, P<0.01; ORadjusted=3.30, 95% CI, 1.58-6.87, P<0.01). In the multiple CpG site methylation (MCSM) analysis, a high MCSM value denoted an increased CRC risk (ORadjusted=4.97, 95% CI, 3.34-7.37, P<0.01). CONCLUSION: In peripheral blood, the methylation of JAK2, STAT1, and high levels of MCSM are promising biomarkers for CRC risk.

Discovery and validation of tissue-specific DNA methylation as noninvasive diagnostic markers for colorectal cancer.

BACKGROUND: Noninvasive diagnostic markers that are capable of distinguishing patients with colorectal cancer (CRC) from healthy individuals or patients with other cancer types are lacking. We report the discovery and validation of a panel of methylation-based markers that specifically detect CRC. METHODS: This was a large-scale discovery study based on publicly available datasets coupled with a validation study where multiple types of specimens from six cohorts with CRC, other cancer types, and healthy individuals were used to identify and validate the tissue-specific methylation patterns of CRC and assess their diagnostic performance. RESULTS: In the discovery and validation cohort (N = 9307), ten hypermethylated CpG sites located in three genes, C20orf194, LIFR, and ZNF304, were identified as CRC-specific markers. Different analyses have suggested that these CpG sites are CRC-specific hypermethylated and play a role in transcriptional silencing of corresponding genes. A random forest model based on ten markers achieved high accuracy rates between 85.7 and 94.3% and AUCs between 0.941 and 0.970 in predicting CRC in three independent datasets and a low misclassification rate in ten other cancer types. In the in-house validation cohort (N = 354), these markers achieved consistent discriminative capabilities. In the cfDNA pilot cohort (N = 14), hypermethylation of these markers was observed in cfDNA samples from CRC patients. In the cfDNA validation cohort (N = 155), the two-gene panel yielded a sensitivity of 69.5%, specificity of 91.7%, and AUC of 0.806. CONCLUSIONS: Hypermethylation of the ten CpG sites is a CRC-specific alteration in tissue and has the potential use as a noninvasive cfDNA marker to diagnose CRC.

DNA Methylation of Imprinted Genes KCNQ1, KCNQ1OT1, and PHLDA2 in Peripheral Blood Is Associated with the Risk of Breast Cancer.

Methylation alterations of imprinted genes lead to loss of imprinting (LOI). Although studies have explored the mechanism of LOI in breast cancer (BC) development, the association between imprinted gene methylation in peripheral blood and BC risk is largely unknown. We utilized HumanMethylation450 data from TCGA and GEO (n = 1461) to identify the CpG sites of imprinted genes associated with BC risk. Furthermore, we conducted an independent case-control study (n = 1048) to validate DNA methylation of these CpG sites in peripheral blood and BC susceptibility. cg26709929, cg08446215, cg25306939, and cg16057921, which are located at KCNQ1, KCNQ1OT1, and PHLDA2, were discovered to be associated with BC risk. Subsequently, the association between cg26709929, cg26057921, and cg25306939 methylation and BC risk was validated in our inhouse dataset. All 22 CpG sites in the KCNQ1OT1 region were associated with BC risk. Individuals with a hypermethylated KCNQ1OT1 region (>0.474) had a lower BC risk (OR: 0.553, 95% CI: 0.397−0.769). Additionally, the methylation of the KCNQ1OT1 region was not significantly different among B cells, monocytes, and T cells, which was also observed at CpG sites in PHLDA2. In summary, the methylation of KCNQ1, KCNQ1OT1, and PHLDA2 was associated with BC risk, and KCNQ1OT1 methylation could be a potential biomarker for BC risk assessment.

Methylation of Immune-Related Genes in Peripheral Blood Leukocytes and Breast Cancer.

Abnormal DNA methylation contributes to breast cancer (BC). Immune-related genes play crucial roles in BC development and progression. This study aims to investigate the effect of methylation of immune-related genes in peripheral blood leukocytes (PBLs) on BC risk. GSE51032 and GSE104942 datasets were used to identify significantly differentially methylated CpG sites (DMCs) of immune-related genes. A case-control study was conducted using MethylTarget sequencing to validate the relationship between the methylation levels of the screened genes and BC risk. We also evaluated the association between methylation haplotypes of screened genes and BC risk. Moreover, we sorted the blood leukocytes into T cells, B cells, and monocytes to detect the difference of DNA methylation in different cell subtypes. A total of five DMCs were screened from GEO datasets, including cg01760846 (PSMC1), cg07141527 (SPPL3), cg15658543 (CARD11), cg21568368 (PSMB8), and cg24045276 (NCF2). In the case-control study, there were significant associations between methylation of the CpG sites in the five genes and BC risk. Methylation haplotype burdens of PSMC1, CARD11, and PSMB8 were associated with reduced BC risk. Moreover, there were heterogeneities in the methylation levels of the genes in different cell subtypes. In conclusion, methylation of PSMC1, SPPL3, CARD11, PSMB8, and NCF2 in PBLs were associated with BC risk. The five-gene methylation could be the potential biomarkers for predicting BC risk.

Inhibitory immune checkpoints PDCD-1 and LAG-3 hypermethylation may reduce the risk of colorectal cancer.

BACKGROUND: Changes in DNA methylation of immunosuppressive checkpoints may impact express and consequently affect antigen processing and presentation by tumor cells and facilitates evasion of immunosurveillance and lead to colorectal cancer (CRC). This study is to investigate the effect of PDCD-1, LAG-3 methylation statuses in peripheral blood leukocytes on CRC risk. METHODS: GSE51032 dataset from Gene Expression Omnibus comprised of 166 CRC patients and 424 normal samples was used to identify significantly differentially methylated CpG sites of the two genes. A case-control study with 390 CRC patients and 397 cancer-free controls was carried out to validate the relationship between the methylation levels of the two genes and CRC susceptibility and then estimated their interactions with environmental factors on CRC risk. RESULTS: In the GSE51032 dataset, cg06291111 (PDCD-1) and cg10191002 (LAG-3) were screened as the candidate CpG sites for the following study. There were significant associations between hypermethylation of PDCD-1 and LAG-3 and lower risk of CRC (ORadj = 0.322, 95% CI 0.197-0.528; ORadj = 0.666, 95% CI 0.446-0.5996, respectively). Moreover, the results in case-control study showed similar trend, that hypermethylation of PDCD-1 and LAG-3 were associated with lower CRC risk (ORadj = 0.448, 95% CI 0.322-0.622; ORadj = 0.417, 95% CI 0.301-0.578, respectively). A synergistic interaction between LAG-3 hypermethylation and intake of eggs on CRC risk was observed. There were combination effects between hypermethylation of PDCD-1 and LAG-3 and environmental factors on CRC risk. CONCLUSIONS: PDCD-1 and LAG-3 may potentially serve as blood-based predictive biomarkers for CRC risk.

A panel of differentially methylated regions enable prognosis prediction for colorectal cancer.

We aim to identify a panel of differentially methylated regions (DMRs) for predicting survival outcomes for patients with CRC from the TCGA (n = 393). Four DMRs (MUC12, TBX20, CHN2, and B3GNT7) were selected as candidate prognostic markers for CRC. The prediction potential of selected DMRs was validated by the targeted bisulfite sequencing method in an independent cohort with 251 Chinese CRC patients. DMR methylation scores (DMSs) were constructed to evaluate the prognosis of CRC. Results of the validation cohort confirmed that higher DMSs were associated with poor overall survival (OS) of CRC, with hazard ratio (HR) value ranged from 1.445 to 2.698 in multivariable Cox models. Patients in the high prognostic index (high-PI) group showed a markedly unfavorable prognosis compared to the low-PI group in both TCGA discovery cohort (HR = 3.508, 95%CI: 2.196-5.604, P < 0.001) and independent validation cohort (HR = 1.912, 95%CI: 1.258-2.907, P = 0.002).

Methylation of three genes encoded by X chromosome in blood leukocytes and colorectal cancer risk.

X chromosome change has been proved to be associated with carcinogenesis and related to gender differences in cancer risk. If aberrant methylation of genes encoded by X chromosome involve in the risk and prognosis of cancers, including colorectal cancer (CRC), remain unclear. We conducted a case-control study consisted of 432 CRC cases and 434 controls, detecting the methylation levels of FAM156B, PIH1D3, and PPP1R3F in the X chromosome in blood leukocytes using methylation-sensitive high-resolution melting (MS-HRM). We analyzed the relationship between the methylation levels and CRC susceptibility and then explored the interactions with environmental factors on CRC risk with logistics regression. Moreover, we conducted a follow-up study containing 225 CRC patients to explore the associations between the methylation of FAM156B, PPP1R3F, and PIH1D3 and CRC prognosis. The hypermethylation of FAM156B, PPP1R3F, and PIH1D3 was related to increased CRC risk (ORPS-adj  = 2.932, 95% confidence interval [CI]: 2.029-4.237; ORPS-adj  = 1.602, 95% CI: 1.078-2.382; ORPS-adj  = 1.628, 95% CI: 1.065-2.490, respectively). In the multiple CpG site methylation (MCSM) analysis, compared with non-MCSM, a significant relationship between MCSM and increased CRC risk was found (ORPS-adj  = 2.202, 95% CI: 1.512-3.208). We observed synergistic interaction between PPP1R3F hypermethylation and fried food consumption on CRC risk (ORi  = 2.682, 95% CI: 1.321-5.446). However, there were no associations between the methylation of FAM156B, PPP1R3F, and PIH1D3 and CRC prognosis (p > 0.05). In conclusion, the methylation of FAM156B, PPP1R3F, and PIH1D3 genes in blood leukocytes is significantly related to CRC risk and may be potential biomarkers for CRC risk but not prognosis.

Development and validation of 3-CpG methylation prognostic signature based on different survival indicators for colorectal cancer.

Abnormal DNA methylation is considered a vital hallmark to regulate gene expression and influence the development and progression of colorectal cancer (CRC). Although CRC-related methylation prognostic models have been developed, their clinical application is limited due to the lack of external validation and extension to other survival evaluation indicators. Therefore, this study aimed to develop and validate novel methylation prognostic models correlated with different survival indicators for individualized prognosis prediction for CRC patients. The prognostic-related CpG sites of methylation-driven genes screened by the MethylMix algorithm were identified and validated in The Cancer Genome Atlas (TCGA) CRC methylation data and our methylation data. The prognostic models correlated with different survival evaluation indicators (overall survival [OS] and disease-free survival [DFS]) were developed and validated in the TCGA CRC dataset (N = 376) and our independent CRC dataset (N = 227). We utilized the combination of selected 3-CpG methylation sites in three genes (DAPP1, FAM3D, and PIGR) to construct a prognostic risk-score model. In the training dataset, Kaplan-Meier survival analysis demonstrated that high-risk patients had significantly poorer survival than low-risk patients (pOS = .0014; pDFS < .001). Then, the 3-CpG methylation signature was successfully validated as an independent predictor in the testing data set (pOS = .016; pDFS = .016). A prognostic nomogram was constructed and validated. Additionally, mediation analysis revealed the direct effect of the methylation signature on CRC prognosis (pOS = 9.149e-06; pDFS = .001). In summary, our study revealed that the 3-CpG methylation signature might be a potential prognostic indicator to facilitate individualized survival prediction for CRC patients.

Tsukushi is a novel prognostic biomarker and correlates with tumor-infiltrating B cells in non-small cell lung cancer.

A recent study has reported that tsukushi (TSKU) may be related to the development of lung cancer. However, few studies focused on if TSKU associated with the prognosis and immune infiltration cells in non-small cell lung cancer (NSCLC). The effect of TSKU expression on prognosis with NSCLC was analyzed in the PrognoScan database and validated in The Cancer Genome Atlas. The composition of tumor infiltrating cells was quantified by methylation and expression data. We combined levels of tumor infiltrating cells with TSKU to evaluate the survival of patients. The analysis of a cohort (GSE31210, N=204) of lung cancer patients demonstrated that high TSKU expression was strongly associated with poor overall survival (P =1.90E-05). The combination of high TSKU expression and low infiltration B cells identified a subtype of patients with poor survival in NSCLC. Besides, the proportion of B cells in NSCLC patients with TSKU hypermethylation were higher than those patients with TSKU hypomethylation (P <0.001). Overall, high TSKU expression combined with low infiltration of B cells may associate with a poor prognosis of NSCLC patients. TSKU might be a potential prognostic biomarker involved in tumor immune infiltration in NSCLC.

Association between plasma prostaglandin E2 level and colorectal cancer.

Evidences for the personalized use of nonsteroidal anti-inflammatory drugs (NSAIDs) in colorectal cancer (CRC) prevention and treatment that include consideration of prostaglandin E2 levels are necessary. This study was designed as a case-control study including 60 CRC patients and 120 cancer-free controls. A sensitive empirical method, precolumn derivatization HPLC, was used to determine plasma PGE2 levels. The TaqMan SNP Genotyping Assay was used for the genotyping of prostaglandin-endoperoxide synthase 2 (PTGS2) polymorphisms. Multivariate logistic regression analysis suggested that 1 log10(PGE2) increase would result in a 3.64-fold increase in the risk of CRC. Moreover, subjects with log10(PGE2) level in the 75th percentile had a significantly higher risk of CRC than those with log10(PGE2) levels in the 25th percentile [odds ratio (OR), 3.50; 95% confidence interval (CI), 1.35-9.05]. This association was more evident after adjustment for history of NSAIDs use (OR, 3.85; 95% CI, 1.46-10.16). Preliminarily, 260.02 and 414.95 pg/ml might be proposed as the preventive and warning cutoff values of plasma PGE2 for CRC. The preferred NSAIDs dose for patients with the AG+GG (rs689466) and CC+CT (rs5275) genotypes should be higher than that of patients carrying AA or TT genotypes, despite the presence of equal plasma PGE2 levels. We show for the first time that the plasma PGE2 level is associated with the risk of CRC. We provide a preliminary suggestion for NSAIDs doses adjustment according to PTGS2 genotypes after consideration of plasma PGE2 levels.

Colorectal cancer patients with CASK promotor heterogeneous and homogeneous methylation display different prognosis.

Homogenous DNA methylation clearly affects clinical outcomes. However, less is known about the effects of heterogeneous methylation. We aimed to investigate the different effects between CASK promoter methylation heterogeneity and homogeneity on colorectal cancer (CRC) patients' prognosis. The methylation status of CASK in 296 tumor tissues and 255 adjacent normal tissues were evaluated using Methylation-sensitive high-resolution melting (MS-HRM). Digital MS-HRM (dMS-HRM) visualized heterogeneous methylation and subsequent sequencing provided exact patterns. Log-rank test and Cox regression model were adopted to assess the association between CASK methylation status and CRC prognosis with propensity score (PS) method to control confounding biases. Heterogeneous methylation was detected in both tumor (52.2%) and non-neoplastic tissue surrounding the tumor (62.4%). It occurred more frequently in lower levels of tumor invasion (P = 0.002) and male patients (P < 0.001). Compared with heterogeneous methylation, patients with CASK homogeneous methylation presented poorer overall survival (OS) (HR: 1.919, 95% CI: 1.146-3.212, P = 0.013) and disease-free survival (DFS) (HR: 1.913, 95% CI: 1.146-3.194, P = 0.013). This unfavorable effect still existed among older (≥ 50), Dukes staging C/D, and rectal cancer patients. MS-HRM and dMS-HRM when combined can assess the degree and complexity of heterogeneous methylation with a visible pattern.

DNA Methylation in RARß Gene as a Mediator of the Association Between Healthy Lifestyle and Breast Cancer: A Case-Control Study.

PURPOSE: Lifestyle factors and methylation in the retinoic acid receptor ß (RARß) gene are associated with breast cancer (BC). This study aims to examine the mediation effect of RARß methylation on the association between healthy lifestyle and BC in Chinese women. PATIENTS AND METHODS: This case-control study consisted of 408 BC patients and 573 controls. A healthy lifestyle score (HLS) was constructed based on diet, alcohol use, physical activity, body mass index and smoking. The mediation effect of RARß methylation in peripheral blood leukocytes was assessed in a causal mediation model using R package Lavaan. RESULTS: A higher HLS was significantly associated with lower risk of BC (P-value<0.001). In mediation analyses, the total effect of HLS on BC measured as a regression coefficient was significant (-0.237). The indirect effects of HLS on RARß methylation (-0.153) and RARß methylation on BC (0.220) were both significant. The significant mediation effect of RARß methylation on the HLS-BC association was estimated at 14.3%. CONCLUSION: The relationship between healthy lifestyle and BC is partly mediated by RARß methylation, suggesting that epigenetic modifications play a role in the underlying mechanisms in response to lifestyles and contribute to the development of BC.

Specific DNA methylation markers in the diagnosis and prognosis of esophageal cancer.

The early diagnosis and accurate prognosis prediction of esophageal cancer is an essential part of improving survival. However, these diseases lack effective and specific markers. A total of 1,744 samples of HumanMethylation450 data were integrated to identify and validate specific methylation markers for esophageal adenocarcinoma (EAC) and esophageal squamous cell carcinoma (ESCC) as well as for Barrett's esophagus (BE) using The Cancer Genome Atlas and the Gene Expression Omnibus. The diagnostic and prognostic methylation classifiers were constructed by moderated t-statistics and the least absolute shrinkage and selection operator method. The diagnostic methylation classifier using 12 CpG sites was constructed in training set (377 samples) that could effectively discriminate samples of BE, EAC, and ESCC from normal tissue (AUC = 0.992), which achieved highly predictive ability in both internal (187 samples, AUC = 0.990) and external validation (184 samples, AUC = 0.978). The prognostic methylation classifier with 3 CpG and 2 CpG sites for EAC and ESCC respectively, could accurately estimate the prognosis of an individual patient and improved the predictive ability of the tumor node metastasis staging system. Overall, our study systematically analyzed large-scale methylation data and provided promising markers for the diagnosis and prognosis of esophageal cancer.

DNA methylation of SFRP1, SFRP2, and WIF1 and prognosis of postoperative colorectal cancer patients.

BACKGROUND: As biomarkers, DNA methylation is used to detect colorectal cancer (CRC) and make assessment of CRC prognosis. The published findings showed the association between the methylation of SFRP1, SFRP2, and WIF1, located in the Wnt signaling pathway, and the prognosis of CRC were not consistent. Our study aimed to explore the potential possibility of SFRP1, SFRP2, and WIF1 concomitant promoter methylation as prognostic biomarkers of postoperative CRC patients. METHODS: As a total of 307 sporadic postoperative CRC patients were followed up, we detected SFRP1, SFRP2, and WIF1 methylation obtained from tumor tissues and adjacent non-tumor tissues respectively on the basis of methylation-sensitive high resolution melting analysis. Univariate and multivariate Cox regressions were carried out so as to assess the potential possibility of SFRP1, SFRP2, and WIF1 promoter methylation as predictors of prognosis. Confounders in our study were controlled by Propensity Score (PS) analysis. RESULTS: The SFRP1, SFRP2, and WIF1 methylation levels in tumor tissues were significantly higher than that in adjacent non-tumor tissues (P < 0.001). SFRP2 hypermethylation was significantly associated with a favorable clinical outcome at the hazard ratio (HR) of 0.343 [95% confidence intervals (CI): 0.164-0.718, P = 0.005] and 0.410 (95% CI: 0.200-0.842, P = 0.015) in multivariate Cox regression and PS analysis, respectively. Co-hypermethylation of SFRP1 and SFRP2 was significantly associated with a favorable clinical outcome at the HR of 0.333 (95% CI: 0.159-0.694, P = 0.003) and 0.398 (95% CI: 0.192-0.821, P = 0.013) in multivariate Cox regression and PS analysis, respectively. Co-hypermethylation of SFRP1, SFRP2 and WIF1 was significantly associated with a favorable clinical outcome at the HR of 0.326 (95% CI: 0.117-0.908, P = 0.032) and 0.401 (95% CI: 0.146-1.106, P = 0.077) in multivariate Cox regression and PS analysis, respectively. CONCLUSIONS: SFRP1, SFRP2, and WIF1 were frequently hypermethylated in CRC tumor tissues. It was apparent that the promoter hypermethylation of SFRP2 and co-hypermethylation of SFRP1 and SFRP2 might be considered as independent prognostic predictors for survival advantage of postoperative CRC patients.

Diet quality score and survival rate in patients with colorectal cancer.

BACKGROUND AND OBJECTIVES: Results regarding associations between specific-food and prognosis of colorectal cancer (CRC) are limited and inconsistent, and few studies have examined this issue in Asian population. This study examined the association between diet and prognosis of CRC, and developed a diet quality score for prognosis of CRC. METHODS AND STUDY DESIGN: 352 participants who provided completed dietary information were recruited during 2004 to 2014, and there are 154 death case documented with 10-year follow-up. Cox regression models were used to examine associations between food groups and survival rate, and to develop the diet quality score for prognosis of CRC. RESULTS: Intake of whole grain, fruit and coffee consumption habitus were associated with higher survival rate (HR 0.56 [95% CI 0.35, 0.89] for whole grain; HR 0.62 [95% CI 0.40, 0.97] for fruit; HR 0.46 [95% CI 0.24, 0.87] for coffee), whereas intake of red meat and frequency of grilled food were associated with lower survival rate (HR 1.68 [95% CI 1.08, 2.61] for red meat; HR 1.78 [95% CI 1.05, 3.02] for grilled food). The overall diet quality based on these nutritional factors was negatively associated with survival rate (HR 1.60 [95% CI 1.07, 2.39] with adjustment for age, sex, BMI, smoking, drinking, energy intake, UICC stage, chemotherapy, postoperative adjuvant radiotherapy, tumor size, carcinoembryonic antigen and carbohydrate antigen 19-9 levels. CONCLUSIONS: Whole grain, fruit, red meat, coffee consumption habitus and frequency of grilled food were significantly associated with survival rate in Chinese population. The diet quality score may be useful for Chinese healthcare providers to advise patients on the optimal diet.

Bisphosphonates and primary breast cancer risk: an updated systematic review and meta-analysis involving 963,995 women.

IMPORTANCE: Prevention of primary breast cancer (BCa) in women is of great public health importance. The existing results from observational epidemiologic studies focused on the association between bisphosphonates and primary BCa risk have been inconsistent. OBJECTIVE: To update this systematic review and meta-analysis to assess the effect of bisphosphonates on primary BCa risk. DATA SOURCES: We comprehensively searched MEDLINE, EMBASE, Cochrane libraries, ProQuest, and Web of Science through June 25, 2018 for relevant studies. STUDY SELECTION: Epidemiological studies that assessed the effect of bisphosphonates on the risk of primary BCa in women. DATA EXTRACTION AND SYNTHESIS: We reported this meta-analysis according to the PRISMA guidelines. Available multivariable-adjusted effect estimates and corresponding 95% CIs were pooled with a random-effects model. MAIN OUTCOMES AND MEASURES: The prespecified main outcome was the risk of primary BCa. RESULTS: In total, five cohort studies involving 657,558 women and 12,991 primary BCa patients, three population-based case-control studies involving 54,701 primary BCa cases and 237,962 healthy controls and two randomized controlled trials (RCTs) involving 13,774 women and 165 primary BCa patients were included in this meta-analysis. Bisphosphonates were associated with a 12% decreased risk of primary BCa (RR, 0.88; 95% CI, 0.83-0.94). However, when we analyzed study designs separately, the pooled results from observational studies were inconsistent with that from RCTs. The observed association of primary BCa risk with long-term use (≥1 year) of bisphosphonates seemed to be more robust and stronger than that of short-term use (<1 year) (RR, 0.75; 95% CI, 0.66-0.84; and 0.90; 95% CI, 0.84-0.97; respectively). CONCLUSION: This meta-analysis adds to the body of evidence for an association between bisphosphonates and a significantly decreased risk of primary BCa. However, future large-scale RCTs are required to validate this concern.