Diabetes and Metformin Association with Recurrence Score in a Large Oncotype Database of Breast Cancer Patients

The Oncotype DX® (ODX) is a genomic assay that provides clinicians with a prediction of benefit of chemotherapy in node-negative, tamoxifen-treated breast cancer. However, the relationship between ODX recurrence score (RS) and diabetes, a common comorbidity in breast cancer patients, has been inadequately described in the literature. Specifically, the association of diabetes treatment with metformin and RS is inconclusive, with different studies reporting conflicting results. Because diabetes has been associated with higher RS, it has been suggested that management of diabetes with metformin in breast cancer patients may be associated with a lower RS. Objectives: We studied a large cohort of early-stage, hormone-positive breast cancer patients to determine if there is an association between RS and metformin treatment. Methods: In this study, we retrospectively examined the medical records of 514 early-stage, hormone-positive breast cancer patients who had oncotype testing performed between 2007 and 2017. Number (%) or median were used to describe the patients' characteristics between groups and were compared by the Kruskal-Wallis test at a significance level of 5%. Results: Of this cohort, 67 (13%) had a diabetes diagnosis at the time of breast cancer diagnosis, including both diabetes mellitus and pre-diabetes. The median RS for non-diabetic patients was 16 and the median RS for diabetic patients was 15. This difference was not significant, nor was there a statistical difference in RS between diabetic patients taking metformin (median RS = 15) and diabetic patients not taking metformin (median RS = 15). These results held true even when controlling for BMI. Conclusions: We conclude that neither diabetes diagnosis nor metformin use is associated with a difference in oncotype RS in this population of diabetic patients.