HealthDay News– Risk for developing breast cancer in patients with type 2 diabetes (T2D) may be influenced by long-term metformin use, according to a study published online in the Annals of Oncology.

Yong-Moon Mark Park, MD, PhD, from the National Institutes of Health in Research Triangle Park, North Carolina, and colleagues used data from 44,541 Sister Study participants aged 35 to 74 years at enrollment to examine T2D and antidiabetic medications in relation to breast cancer risk.

A total of 2678 breast cancers were diagnosed during follow-up. The researchers identified no overall association between T2D and breast cancer risk (hazard ratio [HR], 0.99; 95% confidence interval [CI], 0.87 to 1.13). However, an increased risk for triple-negative breast cancer was seen in association with T2D (HR, 1.40; 95% CI, 0.90 to 2.16).

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T2D with metformin use was not associated with overall breast cancer risk compared with not having T2D (HR, 0.98; 95% CI, 0.83 to 1.15), but there was an association seen for a reduced risk for ER-positive breast cancer (HR, 0.86; 95% CI, 0.70 to 1.05) and an increased risk for ER-negative (HR, 1.25; 95% CI, 0.84 to 1.88) and triple-negative breast cancer (HR, 1.74; 95% CI, 1.06 to 2.83).

“The report by Park adds to the growing evidence linking T2D and its treatment to breast cancer risk but definitive conclusions regarding these associations are not yet possible,” write the authors of an accompanying editorial.

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