Metformin Improves Outcomes In Patients with Diabetes and Breast Cancer

Metformin might improve the prognosis of women with diabetes who have human epidermal growth factor receptor-2 [HER2] positive and hormone receptor–positive breast cancer, according to the findings of a new study.

The substudy included 8381 patients with HER2-positive breast cancer enrolled in the ALTTO trial who were randomly assigned to receive either trastuzumab, lapatinib, lapatinib and trastuzumab together, or a sequence of the 2 agents for 1 year. A total of 7935 patients (94.7%) had no history of diabetes when diagnosed with cancer, 186 (2.2%) patients had diabetes when diagnosed with cancer but had not been treated with metformin, and 260 (3.1%) patients had diabetes that had been treated with metformin when diagnosed with cancer.

Over a median of 4.5 years of follow-up, 1205 patients (14.38%) experienced disease-free survival (DFS), 929 (11.08%) experienced distant disease-free survival (DDFS), and 528 (6.3%) experienced overall-survival (OS).
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The researchers found that patients with diabetes who were not treated with metformin had worse DFS, DDFS, and OS. While no significant associations between metformin treatment in patients with diabetes and breast cancer were found for long-term DFS, DDFS, and OS, patients with hormone receptor-positive breast cancer and diabetes treated with metformin had better outcomes compared with those not treated with metformin.

Diabetes did not influence survival outcomes in patients with hormone receptor-negative status breast cancer.

In addition, the researchers found that insulin treatment was associated with detrimental effects in patients with diabetes and hormone receptor-positive breast cancer.

“Despite the lack of level one evidence, we believe that for patients with diabetes and HER2-positive and hormone receptor–positive disease, it is reasonable to recommend metformin treatment if patients have not already received treatment and to avoid as much as possible insulin use,” the researchers concluded. “From a prognostic point of view, patients with diabetes and HER2-positive and hormone receptor–positive disease who are treated with insulin should be considered at higher risk of recurrence.”

—Melissa Weiss

Reference:

Sonnenblick A, Agbor-Tarh D, Bradbury I, et al. Impact of diabetes, insulin, and metformin use on the outcome of patients with human epidermal growth factor receptor-2 positive primary breast cancer: analysis from the ALTTO phase II randomized trial [published online May 2017]. J Clin Oncol. doi:10.1200/JCO.2016.69.7722