Association between metformin use and progression of monoclonal gammopathy of undetermined significance to multiple myeloma in US veterans with diabetes mellitus: a population-based retrospective…

Su-Hsin Chang, Suhong Luo, Katiuscia K O'Brian, Theodore S Thomas, Graham A Colditz, Nils P Carlsson, Kenneth R Carson

Multiple myeloma (MM) is one of the most common hematologic malignancies in the United States and is consistently preceded by monoclonal gammopathy of undetermined significance (MGUS). A retrospective cohort of patients in the U.S. Veterans Health Administration database diagnosed with MGUS between 1, October, 1999 and 31, December, 2009 and diabetes mellitus prior to their MGUS diagnosis was identified and followed through 6, August, 2013. Patient-level clinical data were reviewed to verify diagnoses and to abstract data on size of baseline M-protein and type of MGUS, i.e., immunoglobulin (Ig) subtype or light-chain, when available. Metformin users were defined as patients that were prescribed metformin for at least 4 years, with no single break between consecutive prescriptions ≥6 months. Kaplan-Meier curves and Cox models were used to analyze the association between metformin use and the progression of MGUS to MM. The analytic cohort consisted of 2,003 MGUS patients with a median follow-up time of 69 months. Within the analytic cohort, 463 metformin users (23·1%) were identified. Among the metformin users, 13 patients progressed to MM, while 74 patients progressed to MM among the non-metformin users. Metformin use was associated with a reduced risk of transformation to MM (Hazard ratio, HR: 0·47; 95% confidence interval, CI: 0·25-0·87). For diabetics diagnosed with MGUS, metformin use for 4 years or longer was associated with a reduced risk of transformation of MGUS to MM. Prospective studies are required to determine whether this association is causal and whether these results can be extrapolated to non-diabetics.