Diabetes mellitus and pancreatic cancer in a population-based case-control study in the San Francisco Bay Area, California

Background: Diabetes has been postulated to be both a risk factor and a consequence of pancreatic cancer, but the degree of risk and associated clinical factors remain unclear. Methods: We conducted a population-based case-control study of pancreatic cancer in the San Francisco Bay Area between 1995 and 1999. Rapid case ascertainment through the Surveillance, Epidemiology and End Results registry for cases and random selection from the general population for controls were employed to identify study participants with no proxy interviews. Results: Five hundred thirty-two cases and 1,701 controls were interviewed. Participants with pancreatic cancer were more likely to report a history of diabetes (13%) than were controls [9%; odds ratio (OR), 1.5; 95% confidence interval (95% CI), 1.1-2.1]. Compared with diabetics in the control group, diabetics in the case group had a shorter duration of diabetes (P = 0.0003) and a larger proportion of insulin users (P = 0.002). Risk for pancreatic cancer varied with duration of diabetes (OR, 2.4; 95% CI, 1.4-4.0 for 1-4 years; OR, 2.0; 95% CI, 1.2-3.4 for 5-9 years; and OR, 0.86; 95% CI, 0.52-1.4 for >= 10 years diabetes duration; P-trend = 0.004). Among diabetics, use of oral diabetes medication or insulin for >= 5 years was not associated with pancreatic cancer, but insulin use of < 5 years was associated with a 6.8-fold risk for pancreatic cancer (95% CI, 3.7-12). Conclusion: Recent-onset diabetes may be a complication or an early marker of pancreatic cancer. Diabetes of short duration with insulin use conferred a substantially elevated risk for pancreatic cancer and may reflect insulin resistance that is elicited by pancreatic cancer.