Diabetes, related factors, and breast cancer risk.

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1509 Background: Diabetes and breast cancer are both common conditions in women and may share common risk factors. Methods: To shed clarification on the potential association between diabetes, related factors and breast cancer risk, a comprehensive literature review and formal meta-analysis was carried out, planned, conducted and reported following PRISMA guidelines regarding meta-analysis of observational studies. Variables studies in relation to breast cancer risk were adiposity, physical activity, glycaemic load, glycaemic index, diabetes, IGF-1, fasting glucose, fasting insulin and C-peptide, adiponectin, metformin and glargine use. The Summary Relative Risk (SRR) and the corresponding 95% Confidence Interval (CI) was calculated. Results: For breast cancer at all ages, the calculated risks were as follows: diabetes (SRR=1.23 95% CI (1.12, 1.34); physical activity (SRR=0.88, 95% CI (0.85, 0.92)); glycaemic load (SRR=1.05, 95% CI (1.00, 1.10)); glycaemic index (SRR=1.05, 95% CI (1.00, 1.09)); fasting glucose (SRR=1.14, 95% CI (0.94, 1.37)); serum insulin (SRR=1.26, 95% CI (0.86, 1.84)); c-peptide (SRR=1.29, 95% CI (0.91, 1.82)); adiponectin (SRR=1.16, 95% CI (0.93, 1.46)); metformin (SRR=0.97, 95% CI (0.82, 1.16)); and glargine (SRR=1.10, 95% CI (0.94, 1.30)). An increase of 5 units in Body Mass Index (a weight increase if 14.5 kg in a person 1.70 metres tall) was associated in post-menopausal breast cancer (SRR=1.12, 95% CI (1.08, 1.16)) but not at pre-menopausal ages (SRR=0.83, 95% CI (0.72, 0.95)). Serum insulin was associated with breast cancer at post-menopausal ages but not at pre-menopausal ages whereas with c-peptide there was a significant association at pre-menopausal ages but not post-menopausal. For IGF-1, Hodge’s Standardised Mean Difference (HSMD) was calculated and there was no significant association with breast cancer at all ages (HSMD=-0.026, 95% CI (-0.031, 0.084)), at post-menopausal ages (HSMD=0.007, 95% CI (-0.068, 0.082)) or at pre-menopausal ages (HSMD=-0.065, 95% CI (-0.009, 0.140)). Conclusions: Key risk factors for breast cancer appear to be adiposity and physical activity which are both related to the risk of developing diabetes.