Table 2.
Age- and study site-stratified RR (95% CI) for breast cancer in China Kadoorie Biobank
| Cases | Cases/PYs | RR (95% CI) | |
|---|---|---|---|
| (/100,000) | |||
| Highest education | |||
| No formal school | 339 | 44.64 | 1.00 (reference) |
| Primary school | 570 | 60.18 | 1.17 (1.11 to 1.23) |
| Middle school | 653 | 84.82 | 1.37 (1.24 to 1.51) |
| High school | 505 | 124.5 | 1.60 (1.39 to 1.85) |
| College/university | 220 | 165.2 | 1.87 (1.54 to 2.27) |
| BMI at age < 50 years, kg/m2 | |||
| < 18.5 | 21 | 98.83 | 1.00 (reference) |
| 18.5–23.9 | 357 | 126.42 | 0.95 (0.84 to 1.07) |
| 24.0–27.9 | 187 | 160.42 | 0.90 (0.71 to 1.14) |
| ≥28 | 43 | 135.81 | 0.85 (0.60 to 1.21) |
| BMI at age ≥ 50 years, kg/m2 | |||
| < 18.5 | 36 | 41.07 | 1.00 (reference) |
| 18.5–23.9 | 642 | 66.66 | 1.25 (1.17 to 1.33) |
| 24.0–27.9 | 683 | 94.59 | 1.57 (1.38 to 1.78) |
| ≥28 | 318 | 118.27 | 1.96 (1.62 to 2.38) |
| Height, cm | |||
| < 150.2 | 382 | 51.58 | 1.00 (reference) |
| 150.2–154.1 | 504 | 66.66 | 1.13 (1.09 to 1.18) |
| 154.2–158.1 | 596 | 78.54 | 1.28 (1.18 to 1.39) |
| ≥ 158.2 | 805 | 105.96 | 1.45 (1.28 to 1.65) |
| No. of first-degree relatives diagnosed with overall cancer | |||
| 0 | 1795 | 71.63 | 1.00 (reference) |
| 1 | 402 | 90.71 | 1.10 (0.99 to 1.23) |
| ≥ 2 | 90 | 136.09 | 1.57 (1.27 to 1.95) |
| No. of live birth | |||
| Nulliparous | 45 | 112.79 | 1.78 (1.29 to 2.45) |
| 1 | 1067 | 101.84 | 1.66 (1.40 to 1.96) |
| 2 | 719 | 74.19 | 1.41 (1.22 to 1.62) |
| ≥ 3 | 456 | 47.58 | 1.00 (reference) |
| Age at menarche, years | |||
| < 12 | 187 | 114.7 | 1.52 (1.31 to 1.76) |
| 13–14 | 748 | 88.12 | 1.32 (1.20 to 1.46) |
| 15–16 | 837 | 74.27 | 1.15 (1.09 to 1.21) |
| ≥ 17 | 515 | 58.77 | 1.00 (reference) |
Abbreviations: BMI body mass index, PY person-year, RRs relative risk, CI confidence interval
Cox model was stratified by age at enrollment in 5-year interval (10 groups) and 10 study sites. All predictors above were included in the final model