Table 2

Incidence rate and relative risk of bladder cancer in the metformin and SU cohorts

CharacteristicsCancers, nPYSIR (95% CI), per 100,000 PYSUnadjusted (HR, 95% CI)Fully adjusted* (HR, 95% CI)
SU initiators6639,588166.7 (129.0–212.1)1.00 (referent)1.00 (referent)
Metformin initiators196181,818107.8 (93.2–123.9)0.63 (0.47–0.83)0.81 (0.60–1.09)
Duration of metformin therapy (years)
 <17562,841119.3 (93.9–149.6)1.00 (referent)1.00 (referent)
 1 to <23846,42681.8 (57.9–112.4)0.66 (0.45–0.99)0.68 (0.46–1.02)
 2 to <33328,493115.8 (79.7–162.6)0.92 (0.61–1.40)0.97 (0.64–1.48)
 3 to <41718,51391.8 (53.5–147.0)0.71 (0.42–1.22)0.76 (0.45–1.30)
 4 to <51311,773110.4 (58.8–188.8)0.84 (0.46–1.52)0.91 (0.50–1.66)
 ≥52013,770145.2 (88.7–224.3)0.99 (0.59–1.66)1.02 (0.59–1.75)
  Ptrend0.820.99
Duration of SU therapy (years)
 <13113,749225.5 (153.2–320.0)1.00 (referent)1.00 (referent)
 1 to <2129,972120.3 (62.2–210.2)0.52 (0.27–1.02)0.55 (0.28–1.09)
 2 to <356,06882.4 (267.5–192.3)0.35 (0.14–0.91)0.37 (0.14–0.95)
 3 to <483,943202.8 (87.6–399.7)0.84 (0.38–1.84)0.85 (0.39–1.89)
 4 to <552,507199.4 (64.7–465.3)0.79 (0.30–2.06)0.63 (0.22–1.82)
 ≥553,348149.3 (48.5–348.5)0.53 (0.20–1.41)0.56 (0.21–1.47)
  Ptrend0.250.21
Duration of therapy, metformin vs. SU (years)
 <10.51 (0.33–0.77)0.64 (0.41–1.00)
 1 to <20.65 (0.34–1.25)0.79 (0.41–1.53)
 2 to <31.34 (0.52–3.43)1.70 (0.66–4.39)
 3 to <40.43 (0.19–1.00)0.57 (0.25–1.34)
 4 to <50.54 (0.19–1.51)0.93 (0.30–2.85)
 ≥50.94 (0.35–2.50)1.18 (0.44–3.19)
  Ptrend0.360.26
  • PYS, person-years; IR, incidence rate.

  • * Adjusted for age (<60, 60–69, and 70 years), sex, smoking (ever vs. never), HbA1c level (<7%, 7–7.9%, 8–8.9%, and 9%), and obesity (BMI 30 kg/m2).

  • The test of trend was calculated by entering the duration categories in a Cox regression model as a continuous variable, whereas for analysis of discrete duration intervals, the variable was included as a categorical variable.