Metformin use among type 2 diabetics and risk of pancreatic cancer in a clinic-based case-control study.

A better understanding of the association between diabetes and pancreatic cancer (PC) may inform prevention and/or early detection strategies. Metformin has been associated with reduced risk of certain cancers, including PC, in some observational clinical studies. We assessed whether metformin use was associated with PC risk among those with type 2 diabetes (DM2), and whether metformin use modulated the association between DM2 and risk of PC. In total, 536 PC cases and 869 frequency-matched controls were recruited predominantly from University of California San Francisco medical clinics from 2006 to 2011. Eligible participants completed direct interviews using a structured risk factor questionnaire. The association between metformin use and PC risk was assessed using propensity score-weighted unconditional logistic regression methods in analyses restricted to diabetics and adjusted multivariable logistic models in the total study population. Ever use of metformin was not associated with PC risk in analyses restricted to DM2 (N = 170) participants (adjusted OR: 1.01, 95% CI: 0.61-1.68). In the total study population (N = 1,405) using nondiabetics as the referent group, PC risk was inversely associated with diabetes duration (ptrend  < 0.001). Further, when DM2 participants were grouped by ever/never use of metformin and compared with nondiabetics, metformin use did not affect the association between DM2 and PC risk (never users: OR: 1.44, 95% CI: 0.78-2.67; ever users: OR: 1.19, 95% CI: 0.72-1.99). Results from our clinic-based case-control study suggest that metformin use is not associated with PC risk among those with DM2 and does not alter the association between DM2 and PC risk.