Association of Metformin Use for Diabetes With Outcomes in HER2-Positive Breast Cancer
In an analysis from the phase III ALTTO trial reported in the Journal of Clinical Oncology, Sonnenblick et al found that among patients receiving adjuvant therapy for HER2-positive breast cancer, those with diabetes who received metformin had better outcomes than those who did not receive metformin.
Study Details
In the ALTTO trial, patients were randomized to receive 1 year of trastuzumab (Herceptin) alone, lapatinib (Tykerb) alone, their sequence, or their combination. Among 8,381 patients included in the current analysis, 7,935 patients (94.7%) had no history of diabetes at diagnosis, 186 patients (2.2%) had diabetes with no metformin treatment, and 260 patients (3.1%) had diabetes and had received metformin. Median follow-up was 4.5 years.
Outcomes
On multivariate analysis, compared with patients without diabetes, those with diabetes who had not received metformin had significantly worse disease-free survival (hazard ratio [HR] = 1.40, P = .043), distant disease–free survival (HR = 1.56, P = .013), and overall survival (HR = 1.87, P = .004). The detrimental effect was limited to hormone receptor–positive patients (HR = 2.05, P =.001; HR = 2.62, P < .001; and HR = 3.25, P < .001, respectively). Compared with patients without diabetes, there were no significant differences in these outcomes among diabetic patients who received metformin (HR = 0.97, P = .873; HR = 0.91, P = .638; and HR = 1.15, P = .541, respectively). Insulin treatment was associated with a detrimental effect on outcomes among patients with hormone receptor–positive disease.
The investigators concluded: “Metformin may improve the worse prognosis that is associated with diabetes and insulin treatment, mainly in patients with primary HER2-positive and hormone receptor-positive breast cancer.”
The study was supported by GlaxoSmithKline, National Cancer Institute grants, and Canadian Cancer Society Research Institute grants.
Evandro de Azambuja, MD, PhD, of Institut Jules Bordet, is the corresponding author of the Journal of Clinical Oncology article.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
