The role of metformin for primary prevention in non-elderly diabetic colorectal cancer patients.

Abstract

406 Background: There is growing evidence for the beneficial effect of metformin in reducing the incidence of colorectal cancer (CRC) in diabetic patients. However, no such studies are done in the US population. We conducted a case control study (N=8,046) in non-elderly diabetic adult US population (age 18-64 years) to investigate the role of metformin for the primary prevention of CRC. Methods: MarketScan claims database was used to identify diabetic patients with CRC using ICD-9 codes. Only incident cases of CRC in diabetic patients were included in the study. Two matched controls (matched for age, sex, and geographical region) were selected per case. The exposure to metformin was assessed from prescriptions in the 12 months prior to the earliest date of CRC diagnosis. The primary objective was to assess the odds of having CRC in metformin users as compared nonusers. Adjusted odds ratios (AOR) were calculated by adjusting for multiple potential confounders using conditional logistic regression. Results: The mean age of CRC patients was 56 years, 60% were males. Metformin was prescribed to 38.13% patients. A total of 37% (995/2,682) patients developed CRC in metformin exposed group compared to 62.9% (1,687/2,682) patients in non-metformin exposed group. In a multivariate model, any metformin use was associated with a statistically significant 12% reduced risk of developing CRC (AOR 0.88, 95% CI, 0.79-0.98, p<0.026). Prescribed NSAIDs were also associated with decreased incidence of CRC (AOR 0.84, 95% CI, 0.73-0.97, p=0.019). Variables associated with increased incidence of CRC in the multivariate model were IBD (AOR 1.94, 95% CI, 1.13-3.33, p<0.015); use of insulin (AOR 1.45, 95% CI, 1.27-1.65, p<0.001); coronary artery disease (AOR 1.66, 95% CI, 1.43-1.93, p<0.001). There was no significant relationship between CRC incidence and obesity (AOR 1.19, 95% CI, 0.93-1.53, p=0.158); polycystic ovary disease (AOR 0.32, 95% CI, 0.03-2.76, p=0.3); sulfonylureas (AOR 1.09, 95% CI, 0.96-1.24, p=0.15); thiazolidinediones (AOR 0.94, 95% CI, 0.82-1.08, p=0.41); statins (AOR 0.914, 95% CI, 0.82-1.01, p=0.108). Conclusions: The use of metformin appears to reduce the incidence of CRC in non-elderly diabetic adult US population.