Summary
To clarify the potential association between diabetes, related factors, treatments, and breast cancer risk, a series of meta-analyses was carried out following PRISMA guidelines. For breast cancer at all ages, the risks obtained from prospective studies were: diabetes (SRR = 1.27 [95% CI, 1.16 to 1.39]); physical activity (SRR = 0.88 [0.85 to 0.92]); glycemic load (SRR = 1.05 [1.00 to 1.10]); glycemic index (SRR = 1.05 [1.00 to 1.09]); fasting glucose (SRR = 1.14 [0.94 to 1.37]); serum insulin (SRR = 1.11 [0.75 to 1.85]); c-peptide (SRR = 1.00 [0.69 to 1.46]), and adiponectin (SRR = 1.16 [0.93 to 1.46]). An increase of 5 units in BMI was associated with postmenopausal breast cancer (SRR = 1.12 [95% CI, 1.08 to 1.16]) but not at premenopausal ages (SRR = 0.83 [95% CI, 0.72 to 0.95]). Serum insulin and c-peptide were associated with breast cancer at postmenopausal ages but not at premenopausal. For IGF-1, Hodge’s standardized mean difference (HSMD) was calculated, and there was no significant association with breast cancer (HSMD = 0.026 [95% CI, –0.031 to 0.084]).
The SRR for breast cancer among users of insulin glargine was 1.08 (0.98 to 1.20) and was 0.92 (0.32 to 2.65) when restricted to randomized trials. Among new users, the SRR for breast cancer was 1.09 (0.98, 1.21), and there was no trend of increasing breast cancer risk with increasing duration of use of glargine (β = 0.04) (P = 0.52). Risk of breast cancer in a prospective cohort declined with increasing follow-up, from 1.99 (1.31, 2.03) with 2 years of follow-up, to 1.60 (1.10 to 2.32) with 3 years, 1.50 (1.10 to 2.10) with 4 years and 1.18 (0.84 to 1.66) with 5 years of follow-up. There is no reduction in risk of breast cancer associated with metformin use (SRR = 0.96 [95% CI, 0.85 to 1.08]) even for the longest duration of use (SRR = 0.94 [95% CI, 0.81 to 1.09]).
An association between these 2 common diseases could have important implications for public health, with common risk factors driving further increases in both diseases yet holding the tantalizing possibility for prevention of both.
Disclosure of Interest
None declared.
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