Table 3.
Hazard Ratios and 95% Confidence Intervals for the Association Between Body Mass Index and Breast Cancer Risk Stratified by Baseline Menopausal Hormone Therapy Use Among Postmenopausal Caucasian Women in the Aggregated Sample From 4 US Prospective Studies, 1979–2006
| Nulliparous Women |
Parous Women Aged <25 Years at First Birth |
Parous Women Aged ≥25 Years at First Birth |
|||||||||
| No. of Casesa | HRb | 95% CI | No. of Casesa | HRbc | 95% CI | Pheterogeneityd | No. of Casesa | HRbc | 95% CI | Pheterogeneitye | |
| Body mass index among never users of menopausal hormone therapy, kg/m2 | |||||||||||
| <25 | 312 | 1.00 | Referent | 685 | 1.00 | Referent | 592 | 1.00 | Referent | ||
| 25–<30 | 184 | 1.18 | 0.98, 1.41 | 558 | 1.25 | 1.11, 1.40 | 367 | 1.14 | 1.00, 1.30 | ||
| ≥30 | 128 | 1.30 | 1.05, 1.61 | 463 | 1.55 | 1.36, 1.75 | 0.40 | 210 | 1.21 | 1.02, 1.42 | 0.86 |
| Body mass index among former users of menopausal hormone therapy, kg/m2 | |||||||||||
| <25 | 123 | 1.00 | Referent | 315 | 1.00 | Referent | 241 | 1.00 | Referent | ||
| 25–<30 | 65 | 1.04 | 0.77, 1.42 | 247 | 1.16 | 0.98, 1.38 | 137 | 1.16 | 0.93, 1.43 | ||
| ≥30 | 26 | 0.81 | 0.52, 1.25 | 163 | 1.34 | 1.10, 1.64 | 0.11 | 64 | 1.28 | 0.96, 1.71 | 0.22 |
| Body mass index among current users of menopausal hormone therapy, kg/m2 | |||||||||||
| <25 | 414 | 1.00 | Referent | 1,300 | 1.00 | Referent | 798 | 1.00 | Referent | ||
| 25–<30 | 199 | 1.03 | 0.87, 1.23 | 823 | 1.02 | 0.94, 1.12 | 418 | 1.12 | 0.99, 1.26 | ||
| ≥30 | 99 | 1.02 | 0.81, 1.27 | 402 | 0.98 | 0.87, 1.10 | 0.96 | 158 | 0.99 | 0.83, 1.18 | 0.71 |
Abbreviations: CI, confidence interval; HR, hazard ratio.
First primary invasive and in situ breast cancers.
Estimated from Cox proportional hazards models (SAS PHREG; SAS Institute, Inc., Cary, North Carolina) that used attained age as the time scale. Separate models fit to nulliparous women, parous women aged <25 years at first birth, and parous women aged ≥25 years at first birth. Models include all variables presented in table 2 (except for menopausal hormone therapy), birth year (before 1927, 1927–1932, 1933–1938, 1939 or later), calendar year of entry (before 1987, 1987–1995, 1996 or later), study, and oral contraceptive use (never, ever, missing). Models include missing category for each variable (data not shown).
Further adjusted for number of livebirths (<3, ≥3, missing).
Pheterogeneity between nulliparous women and parous women aged <25 years at first birth based on a Wald test.
Pheterogeneity between nulliparous women and parous women aged ≥25 years at first birth based on a Wald test.