Table 1.
Characteristics of breast cancer cases and matched controls at blood collection in the Nurses’ Health Study II, mean (SD) or %.
| Cases (n = 1057) | Controls (n = 1057) | |
|---|---|---|
| Age at blood collectiona (y) | 44.7 (4.5) | 44.8 (4.4) |
| Age at menarche (y) | 12.4 (1.3) | 12.8 (1.4) |
| Time between sample collection and diagnosis (y) | 8.0 (4.4) | |
| Parity and age at first birth (%): | ||
| Nulliparous | 21.1 | 15.9 |
| 1–2 children, ≥25 y | 39.2 | 34.9 |
| 1–2 children, <25 y | 14.7 | 15.9 |
| 3+ children, <25 y | 11.3 | 16.6 |
| 3+ children, ≥25 y | 13.8 | 14.2 |
| Ever breastfed (%) | 63.1 | 65.0 |
| Family history of breast cancer (%) | 17.4 | 10.8 |
| Personal history of benign breast disease (%) | 22.1 | 15.6 |
| BMI at age 18 (kg/m2) | 20.8 (2.9) | 21.1 (3.1) |
| Weight change between age 18 and blood collection (kg) | 11.6 (12.0) | 12.6 (13.2) |
| Physical activity, MET-h/wk | 18.0 (15.3) | 18.1 (15.5) |
| Alcohol consumption (g/day) | 3.8 (6.9) | 3.3 (5.6) |
| Past/current exogenous hormone useb (%) | 86.3 | 86.7 |
| Menopausal status at blood collectiona (%) | ||
| Premenopausal | 80.2 | 79.7 |
| Postmenopausal | 12.7 | 13.1 |
| Unknown | 7.1 | 7.3 |
| Menopausal status at diagnosisa (%) | ||
| Premenopausal | 42.0 | 42.2 |
| Postmenopausal | 46.4 | 47.1 |
| Unknown | 11.6 | 10.7 |
| Caucasiana (%) | 97.2 | 98.4 |
| Fasting (>8 h) at blood collectiona (%) | 68.7 | 74.7 |
aMatching factor
bOral contraceptive or menopausal hormone therapy