Table I.
Distribution of baseline descriptive characteristics by case and subcohort status (n = 903)
| Characteristic | Cases (n = 407) | Subcohorta (n = 496) | P valueb | ||
|---|---|---|---|---|---|
| Mean ± SD | |||||
| Age (years) at: | |||||
| Blood draw | 67.2±5.7 | 67.3±6.2 | 0.93 | ||
| Menarche | 12.7±1.5 | 12.8±1.4 | 0.35 | ||
| Breast cancer diagnosis | 73.3±6.3 | — | — | ||
| Education (years) | 16.2±4.4 | 15.3±4.2 | 0.003 | ||
| Years between blood draw and breast cancer diagnosis | 6.1±3.0 | — | — | ||
| Years since menopause | 19.8±8.1 | 20.7±8.9 | 0.10 | ||
| BMI (kg/m2) | 26.7 (22.1, 35.4)c | 25.8 (21.0, 34.7)c | 0.03c | ||
| Waist (cm) | 97.1±13.6 | 96.1±15.2 | 0.35 | ||
| Neck BMD | 0.67±0.10 | 0.66±0.11 | 0.06 | ||
| Total hip BMD | 0.79±0.12 | 0.77±0.13 | 0.02 | ||
| Characteristic | N | % | N | % | P valueb |
| Ethnicity | |||||
| Asian/Pacific Islander | 3 | 0.7 | 5 | 1.0 | |
| Black or African American | 9 | 2.2 | 8 | 1.6 | |
| Hispanic or Latino | 3 | 0.7 | 8 | 1.6 | |
| White Caucasian | 386 | 94.8 | 470 | 94.8 | |
| Other | 6 | 1.5 | 5 | 1.0 | 0.66 |
| Trial participation status | |||||
| Screenee-only | 324 | 79.6 | 372 | 75.0 | |
| FIT | 69 | 17.0 | 98 | 19.8 | |
| FLEX | 14 | 3.4 | 26 | 5.2 | 0.20 |
| Family history of breast cancer in first-degree relatives | |||||
| No | 318 | 78.1 | 420 | 84.7 | |
| Yes | 81 | 19.9 | 61 | 12.3 | 0.002 |
| BMI category (kg/m2) | |||||
| <25 | 148 | 36.4 | 210 | 42.3 | |
| 25–29.9 | 139 | 34.2 | 156 | 31.5 | |
| 30–34.9 | 73 | 17.9 | 81 | 16.3 | |
| ≥35 | 43 | 10.6 | 45 | 9.1 | 0.34 |
| Parity/age at first live birth (years) | |||||
| Nulliparous | 50 | 12.3 | 45 | 9.1 | |
| <20 | 35 | 8.6 | 50 | 10.1 | |
| 20–24 | 160 | 39.3 | 213 | 42.7 | |
| 25–29 | 122 | 30.0 | 127 | 25.6 | |
| ≥30 | 38 | 9.3 | 60 | 12.1 | 0.18 |
| Ever breastfed | |||||
| No | 165 | 40.5 | 211 | 42.5 | |
| Yes | 227 | 55.8 | 271 | 54.6 | 0.62 |
| Prior estrogen therapy used (years) | |||||
| Never | 256 | 62.9 | 330 | 66.5 | |
| <1 year | 39 | 9.6 | 48 | 9.7 | |
| 1–4 | 63 | 15.5 | 64 | 12.9 | |
| 5–9 | 17 | 4.2 | 27 | 5.4 | |
| ≥10 | 26 | 6.4 | 23 | 4.6 | 0.48 |
| Alcohol consumption in past month | |||||
| Not at all | 164 | 40.3 | 208 | 41.9 | |
| Once | 50 | 12.3 | 57 | 11.5 | |
| 2–3 times | 69 | 17.0 | 78 | 15.7 | |
| 1–2 days per week | 50 | 12.3 | 45 | 9.1 | |
| 3–4 days per week | 26 | 6.4 | 40 | 8.1 | |
| 5–6 days per week | 21 | 5.2 | 31 | 6.3 | |
| Every day | 27 | 6.6 | 37 | 7.5 | 0.65 |
| Smoking status | |||||
| Never | 215 | 52.8 | 257 | 51.8 | |
| Former | 153 | 37.6 | 183 | 36.9 | |
| Current | 32 | 7.9 | 53 | 10.7 | 0.38 |
Missing values included in the denominator for calculation of above percentages. Frequency of missing values (cases, subcohort): family history of breast cancer (n = 8, 15); BMI (n = 4, 4); parity/age first live birth (n = 2, 1); ever breastfed (n = 15, 14); prior estrogen use (n = 6, 4); smoking status (n = 7, 3).
aIncludes nine incident breast cancer cases (n = 487+9 incident cases).
b P values calculated using t-tests for continuous variables and χ2 for categorical variables.
cMedian (10th, 90th); P value calculated using Wilcoxon rank sum.
dEstrogen pill use; years of use among former users.