Abstract LB-278: Metformin exposure on survival in localized breast cancer patients with type II diabetes mellitus using electronic health records
Authors: Breitenstein Matthew K. , Wang Leiwei , Weinshilboum Richard M. , Pathak Jyotishman 
Published: May 2015

Abstract
Background: Literature addressing metformin exposure post diagnosis of breast cancer hints at a potential protective association on mortality outcomes, although findings have been inconclusive. In this research, we contribute to this body of evidence by using robust clinical indicators to focus on subgroups of breast cancer patients that might be most appropriate for potential metformin treatment.
Methods: Robust breast cancer staging, treatment, and medication exposure attributes were compiled from Mayo Clinic Electronic Health Records and Breast Cancer Registry using a combination of structured queries and natural language processing of clinical notes. A cohort of female Breast Cancer Registry patients having type II diabetes mellitus (T2DM) at breast cancer diagnosis with a median follow-up period of 79.0 months after breast cancer diagnosis was identified (N=350). Univariate and multivariate cox proportional hazard regression analysis were used to model characteristics of BMI at diagnosis, age at diagnosis, metformin, insulin, thiazolidinedione, and sulfonylurea exposure after diagnosis, cancer grade, cancer stage, chemotherapy, hormone therapy, radiotherapy, lumpectomy, and mastectomy. Patients presenting with metastatic breast cancer at diagnosis, receiving immunotherapy for breast cancer treatment, and concurrent metformin and insulin exposure for T2DM treatments were excluded from the analysis cohort.
Results: Univariate analysis independently identified metformin exposure (HR=0.243,p=0.0016), insulin exposure (HR=3.481,p=0.0210), age at breast cancer diagnosis (HR=1.075,p=0.0001), and targeted radiotherapy (HR=0.337,p=0.0082) as having a significant association with all-cause mortality. The multivariate model of metformin exposure (HR=0.274,p=0.0123), insulin exposure (HR=2.502,p=0.1160), age at breast cancer diagnosis (HR=1.043,p=0.0480), and targeted radiotherapy (HR=0.303,p=0.0044) on all-cause mortality demonstrated significant associations for all variables (Wald Chi-Square=25.2916,p&lt;0.0001). A parallel multivariate model demonstrated metformin exposure (HR=0.101,p=0.0323), insulin exposure (HR=5.241,p=0.0265), and targeted radiotherapy (HR=0.292,p=0.0520) as having significant associations with breast cancer-specific mortality.
Discussion: These findings suggest a protective association for metformin and a potential detrimental association for insulin therapy on all-cause and breast cancer-specific mortality amongst non-metastatic breast cancer patients with T2DM. The findings presented include robust clinical indicators for BMI, stage, and grade at diagnosis, post-diagnosis diabetes medication exposure, and endpoints of all cause and breast cancer specific mortality that have not been available in larger population studies. Our findings have potential pharmacogenetic implications for inhibition of localized breast cancer cell growth by targeting downstream components of the adenosine monophosphate-activated protein kinase pathway, the insulin/insulin-like growth factor-1 signaling pathway, and directly and indirectly via additional metabolic pathways with specific drug therapy combinations.
Citation Format: Matthew K. Breitenstein, Leiwei Wang, Richard M. Weinshilboum, Jyotishman Pathak. Metformin exposure on survival in localized breast cancer patients with type II diabetes mellitus using electronic health records. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-278. doi:10.1158/1538-7445.AM2014-LB-278