Study Looks at T2DM, Metformin Use, and Breast Cancer Risk

When medication is needed to obtain blood glucose targets, insulin and metformin are preferred.1 Metformin is preferable to insulin if it provides sufficient glucose control because it is associated with a lower risk for hypoglycemia and weight gain; however, its use might increase the risk for prematurity. When insulin is needed, referral to a specialty center offering team-based care should be considered because of the complexity of insulin dosing in pregnant patients.1 Glyburide may be considered, but more recent studies have associated its use with a higher risk for neonatal hypoglycemia and macrosomia compared with insulin or metformin.1 Other agents have not been adequately studied. Regardless of agent(s) used, patients should be informed that most oral agents cross the placenta, and all lack long-term safety data.1
When medication is needed to obtain blood glucose targets, insulin and metformin are preferred.1 Metformin is preferable to insulin if it provides sufficient glucose control because it is associated with a lower risk for hypoglycemia and weight gain; however, its use might increase the risk for prematurity. When insulin is needed, referral to a specialty center offering team-based care should be considered because of the complexity of insulin dosing in pregnant patients.1

Glyburide may be considered, but more recent studies have associated its use with a higher risk for neonatal hypoglycemia and macrosomia compared with insulin or metformin.1 Other agents have not been adequately studied. Regardless of agent(s) used, patients should be informed that most oral agents cross the placenta, and all lack long-term safety data.1
The risks for breast cancer in women with type 2 diabetes (T2D) may be influenced by long-term metformin use.

HealthDay News — The risks for breast cancer in women with type 2 diabetes (T2D) may be influenced by long-term metformin use, according to a study published online Jan. 28 in the Annals of Oncology.

Yong-Moon Mark Park, M.D., Ph.D., 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 2,678 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 percent 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 percent CI, 0.90 to 2.16). T2D with metformin use was not associated with overall breast cancer risk compared with not having T2D (HR, 0.98; 95 percent 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 percent CI, 0.70 to 1.05) and an increased risk for ER-negative (HR, 1.25; 95 percent CI, 0.84 to 1.88) and triple-negative breast cancer (HR, 1.74; 95 percent 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.

Abstract/Full Text

Editorial