The Metabolic Syndrome Is a Risk Factor for Breast Cancer: A Systematic Review and Meta-Analysis

Background: The metabolic syndrome (MetS) has been associated with the pathogenesis and prognosis of various malignant tumors. In this systematic review and meta-analysis, we explored the relationship between MetS and breast cancer (BC). Methods: Relevant studies were systematically searched on Ovid MEDLINE, Embase, Cochrane database, and PubMed up to September 16, 2019, using “breast cancer” and “metabolic syndrome” as keywords. Eligible studies with clear definition of MetS, available data, and relationships between MetS and BC were evaluated using a risk ratio (RR) and its 95% confidence interval (CI). Results: Twenty-five studies, including 13 cohort studies and 12 case-control studies, met the inclusion criteria, which assessed a total of 392,583 female participants and 19,628 BC patients. The results revealed a statistically significant increase by 52% of the risk of BC in adult females with MetS (RR = 1.49, 95% CI = 1.31–1.70, p < 0.0001). Postmenopausal MetS patients may have a twofold risk to suffer BC (RR = 2.01, 95% CI = 1.55–2.60, p < 0.001). The risk of BC increased markedly with the number of MetS components: RR = 1.00 for 1 component ( p = 0.976), RR = 1.40 for 2 components ( p = 0.121), and RR = 1.98 for >3 components ( p < 0.001). The risk factors associated with BC were obesity, hypertension, and diabetes (RR = 1.33, 1.19, and 1.30 respectively, all p < 0.001). Conclusions: Our study demonstrated that MetS is highly related with BC. In postmenopausal patients with ≥2 MetS components or a combination of obesity, hypertension, and diabetes, routine BC screening could help to detect BC at an early stage.