Table 2.

HRs of gastrointestinal cancer overall in current metformin users compared with current other NIAD users

Prevalent-user designNew-user design
Exposure categoryEvents (N = 1,076)IRHRa (95% CI)HRb (95% CI)Events (N = 612)IRHRa (95% CI)HRb (95% CI)
Current other NIADsc214457Ref.Ref.120556Ref.Ref.
Current metformin6243760.96 (0.81–1.13)0.97 (0.82–1.15)3613910.91 (0.73–1.14)0.79 (0.59–1.06)
Stratified by treatment staged
  Metformin only2773410,83 (0.69–1.01)0.89 (0.73–1.07)2083590.81 (0.63–1.03)0.75 (0.55–1.04)
  Metformin + SU2694321,07 (0.89–1.29)1.07 (0.89–1.29)1174501.06 (0.81–1.39)0.85 (0.60–1.21)
  Metformin + other NIADs152470,74 (0.43–1.26)0.75 (0.46–1.28)113200.97 (0.52–1.82)0.79 (0.34–1.84)
  Metformin + insulin633791,15 (0.86–1.54)1.06 (0.78–1.43)254961.57* (1.00–2.47)0.74 (0.36–1.51)
Stratified by cumulative dosee
  Low2013760.93 (0.76–1.14)1.05 (0.85–1.28)1434290.95 (0.74–1.23)0.78 (0.54–1.11)
  Medium1963430.88 (0.72–1.08)0.89 (0.73–1.10)1093240.76 (0.58–1.01)0.73 (0.51–1.04)
  High2274081.10 (0.90–1.36)0.96 (0.77–1.19)1094301.10 (0.82–1.47)0.91 (0.62–1.34)
Past metformin1943610.95 (0.77–1.16)0.87 (0.70–1.07)1153970.95 (0.72–1.25)0.74 (0.52–1.06)
Past other NIADs442810.66* (0.48–0.92)0.61* (0.44–0.84)161990.41* (0.24–0.69)0.40* (0.21–0.76)
  • Abbreviation: IR, incidence rate per 100,000 person-years.

  • aAge and sex adjusted.

  • bAdjusted for age, sex, use of statins, insulin, history of hospitalization, duration of diabetes, and year of start of follow-up.

  • cExcluding metformin.

  • dFully adjusted model not adjusted for insulin use.

  • eLow: <405 g; Medium: 405–998 g; High: ≥999 g.

  • *Statistically significant with P < 0.05.