Table 2 Incidence rates of breast cancer and hazard ratios by pioglitazone exposure
Pioglitazone use | Incident case number of breast cancer | Cases followed | Person-years | Incidence rate (per 100,000 person-years) | Median follow-up (years) | Model 1 | Model 2 | Model 3 | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
HR | 95% CI | P value | HR | 95% CI | P value | HR | 95% CI | P value | ||||||
Unmatched cohort | ||||||||||||||
 Never users | 1044 | 174,233 | 435,316.89 | 239.83 | 2.82 | 1.000 |  | 1.000 |  | 1.000 |  | |||
 Ever users | 35 | 6926 | 18,238.48 | 191.90 | 2.84 | 0.800 | (0.571–1.120) | 0.1940 | 0.743 | (0.528–1.044) | 0.0867 | 0.758 | (0.539–1.065) | 0.1107 |
Tertiles of cumulative duration of pioglitazone therapy (months) | ||||||||||||||
 Never users | 1044 | 174,233 | 435,316.89 | 239.83 | 2.82 | 1.000 |  | 1.000 |  | 1.000 |  | |||
  < 10.67 | 9 | 2286 | 5854.05 | 153.74 | 2.82 | 0.643 | (0.334–1.238) | 0.1866 | 0.604 | (0.313–1.165) | 0.1325 | 0.620 | (0.321–1.197) | 0.1546 |
 10.67–19.13 | 11 | 2278 | 5996.14 | 183.45 | 2.85 | 0.765 | (0.422–1.385) | 0.3761 | 0.703 | (0.387–1.276) | 0.2462 | 0.716 | (0.394–1.299) | 0.2712 |
  > 19.13 | 15 | 2362 | 6388.28 | 234.81 | 2.84 | 0.978 | (0.588–1.629) | 0.9333 | 0.907 | (0.543–1.515) | 0.7079 | 0.922 | (0.552–1.540) | 0.7555 |
Cumulative duration of pioglitazone treated as a continuous variable | ||||||||||||||
  For every 1-month increment of pioglitazone use | 0.993 | (0.978–1.008) | 0.3395 | 0.990 | (0.975–1.005) | 0.1895 | 0.991 | (0.976–1.006) | 0.2197 | |||||
Matched cohort | ||||||||||||||
 Never users | 41 | 6926 | 17,533.02 | 233.84 | 2.83 | 1.000 |  | 1.000 |  | 1.000 |  | |||
 Ever users | 35 | 6926 | 18,238.48 | 191.90 | 2.84 | 0.818 | (0.521–1.285) | 0.3837 | 0.817 | (0.520–1.282) | 0.3787 | 0.824 | (0.524–1.296) | 0.4026 |
Tertiles of cumulative duration of pioglitazone therapy (months) | ||||||||||||||
 Never users | 41 | 6926 | 17,533.02 | 233.84 | 2.83 | 1.000 |  |  | 1.000 |  | 1.000 |  | ||
 < 10.67 | 9 | 2286 | 5854.05 | 153.74 | 2.82 | 0.658 | (0.320–1.354) | 0.2560 | 0.657 | (0.319–1.351) | 0.2534 | 0.655 | (0.318–1.352) | 0.2529 |
 10.67–19.13 | 11 | 2278 | 5996.14 | 183.45 | 2.85 | 0.781 | (0.402–1.520) | 0.4671 | 0.779 | (0.401–1.516) | 0.4630 | 0.767 | (0.394–1.495) | 0.4357 |
  > 19.13 | 15 | 2362 | 6388.28 | 234.81 | 2.84 | 0.999 | (0.553–1.805) | 0.9968 | 0.997 | (0.552–1.802) | 0.9925 | 1.043 | (0.574–1.895) | 0.8900 |
Cumulative duration of pioglitazone treated as a continuous variable | ||||||||||||||
 For every 1-month increment of pioglitazone use | 0.996 | (0.978–1.013) | 0.6202 | 0.996 | (0.978–1.013) | 0.6174 | 0.996 | (0.979–1.014) | 0.6841 | |||||