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Review
. 2023 May;12(10):11703-11718.
doi: 10.1002/cam4.5545. Epub 2022 Dec 19.

Breast cancer risk for women with diabetes and the impact of metformin: A meta-analysis

Yifan Lu  1 , Ali Hajjar  2 , Vincent L Cryns  3 , Amy Trentham-Dietz  4 , Ronald E Gangnon  5 , Brandy M Heckman-Stoddard  6 , Oguzhan Alagoz  7
Affiliations
Review

Breast cancer risk for women with diabetes and the impact of metformin: A meta-analysis

Yifan Lu et al. Cancer Med. 2023 May.

Abstract

Background: Diabetes mellitus has been associated with increased breast cancer (BC) risk; however, the magnitude of this effect is uncertain. This study focused on BC risk for women with type 2 diabetes mellitus (T2DM).

Methods: Two separate meta-analyses were conducted (1) to estimate the relative risk (RR) of BC for women with T2DM and (2) to evaluate the risk of BC for women with T2DM associated with the use of metformin, a common diabetes treatment. In addition, subgroup analyses adjusting for obesity as measured by body mass index (BMI) and menopausal status were also performed. Studies were identified via PubMed/Scopus database and manual search through April 2021.

Results: A total of 30 and 15 studies were included in the first and second meta-analyses, respectively. The summary RR of BC for women with T2DM was 1.15 (95% confidence interval [CI], 1.09-1.21). The subgroup analyses adjusting BMI and adjusting BMI and menopause resulted in a summary RR of 1.22 (95% CI, 1.15-1.30) and 1.20 (95% CI, 1.05-1.36), respectively. For women with T2DM, the summary RR of BC was 0.82 (95% CI, 0.60-1.12) for metformin users compared with nonmetformin users.

Conclusions: Women with T2DM were more likely to be diagnosed with BC and this association was strengthened by adjusting for BMI and menopausal status. No statistically significant reduction of BC risk was observed among metformin users.

Impact: These two meta-analyses can inform decision-making for women with type 2 diabetes regarding their use of metformin and the use of screening mammography for early detection of breast cancer.

Keywords: breast cancer; diabetes; meta-analysis; metformin; type 2 diabetes.

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Conflict of interest statement

OA has been a paid consultant for Bristol Myers Squibb, Johnson & Johnson, and Exact Sciences, outside of the submitted work. No other conflicts to report.

Figures

FIGURE 1
FIGURE 1
Flow chart of the literature search process for the meta‐analysis estimating the relative risk of breast cancer for women with type 2 diabetes
FIGURE 2
FIGURE 2
Summary of relative risk of breast cancer among women with type 2 diabetes according to study design (CI, confidence interval; IV, inverse variance; SE, standard error)
FIGURE 3
FIGURE 3
Flow chart of the literature search process for the meta‐analysis estimating the relative risk of breast cancer for women using metformin
FIGURE 4
FIGURE 4
Summary of relative risk of breast cancer according to the use of metformin among women with type 2 diabetes (CI, confidence interval; IV, inverse variance; SE, standard error)
See this image and copyright information in PMC

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