Influence of diabetes mellitus on mortality in breast cancer patients

Background: Breast cancer is one of the most common malignant tumours among women worldwide. Besides, diabetes mellitus is also a major health problem in developed countries. This study explores the association between diabetes mellitus and breast cancer patients' survival outcomes. Methods: A systematic literature search in Embase (http://www.embase.com) and MEDLINE (http://www.ncbi.nlm.nih.gov/pubmed) was conducted from January 1960 to April 2014 and systematically identified clinical studies that evaluated the association between breast cancer mortality and diabetes mellitus. Clinical studies investigating the association between diabetes mellitus and breast cancer patients' survival outcomes were included. Results: Twenty publications were chosen for the meta-analysis, of which 16 studies had all-cause mortality data and 12 studies had breast cancer mortality data. Published from 2001 to 2013, all 20 studies followed a total of 2 645 249 patients including more than 207 832 diabetic patients. Pre-existing diabetes mellitus was associated with a 37% increased risk for all-cause mortality in women with breast cancer (hazard ratio (HR) = 1.37; 95% confidence interval (CI): 1.34-1.41; P = 0.02). Diabetes mellitus was associated with a 17% increased risk for breast cancer mortality in women with breast cancer (HR = 1.17; 95% CI: 1.11-1.22; P < 0.01). Conclusions: Women with diabetes mellitus are at higher risk of breast cancer-specific and all-cause mortality after initial breast cancer diagnosis.