Abstract
Observational studies examining the relationship between hypertension and breast cancer risk have reported conflicting findings. We conducted this systematic review and meta-analysis to summarize the evidence regarding the association between hypertension and risk of breast cancer. Eligible studies were identified through a comprehensive literature search of PubMed, EMBASE, and the Cochrane library until August 2016. We included observational studies that reported relative risks (RR) with corresponding 95% confidence intervals (CIs). Results from individual studies were pooled by using a random-effects model. 29 articles of 30 studies, with totally 11643 cases of breast cancer, were eligible for inclusion in the meta-analysis. We observed a statistically significant association between hypertension and increased breast cancer risk (RR: 1.15; 95% CI: 1.08, 1.22). In the subgroup analysis, we found a positive association between hypertension and breast cancer incidence among postmenopausal women (RR: 1.20; 95% CI: 1.09, 1.31). In contrast, hypertension was not associated with risk of breast cancer among premenopausal women (RR: 0.97; 95% CI: 0.84, 1.12) and Asian population (RR: 1.07; 95% CI: 0.94, 1.22).This meta-analysis collectively suggests a significantly association between hypertension and breast cancer risk, specifically for postmenopausal hypertensive women.
Highlights
Two reviewers (H.H. and W.G.) independently evaluated studies for inclusion, and studies were included in the meta-analysis if they met the following criteria: 1) cohort or case control or nested case-control design; 2) the exposure of interest was hypertension, and the outcome of interest was breast cancer risk; 3) the risk estimates, such as relative risks, odds ratios, or hazard ratios that could be transformed into relative risks with 95% confidence intervals (CIs) were reported; 4) potential factors were adjusted for breast cancer risk
The association between hypertension and breast cancer was consistent for case-control and cohort studies, while the positive association was found in postmenopausal women not in premenopausal women
The subgroup analyses indicated the effect of increased breast cancer risk was significant only in postmenopausal women, this might be explained by different estrogen metabolism pathways amongst premenopausal and postmenopausal women[46,47]
Summary
Two reviewers (H.H. and W.G.) independently evaluated studies for inclusion, and studies were included in the meta-analysis if they met the following criteria: 1) cohort or case control or nested case-control design; 2) the exposure of interest was hypertension (blood pressure higher than corresponding cut-off values or taking antihypertensive medications), and the outcome of interest was breast cancer risk; 3) the risk estimates, such as relative risks, odds ratios, or hazard ratios that could be transformed into relative risks with 95% confidence intervals (CIs) were reported; 4) potential factors were adjusted for breast cancer risk. We performed subgroup analysis based on study design, number of breast cancer cases, geographical regions, definition of hypertension, whether data was extracted from metabolic syndrome (Mets) studies and study quality. Publication bias was assessed with the Egger’s regression test[44]
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