Table 1. Demographic Characteristics of Women With Breast Cancer and Women in the Subcohort From a Case-Cohort Study Within B ~ FIT.
| Characteristic | No. (%) | |
|---|---|---|
| Breast cancer cases (n = 405) | Subcohort (n = 495) | |
| Age, y | ||
| <65 | 148 (36.5) | 187 (37.8) |
| ≥65 | 257 (63.5) | 308 (62.2) |
| Race/ethnicity | ||
| Non-Hispanic white | 384 (94.8) | 469 (94.7) |
| Other | 21 (5.2) | 26 (5.3) |
| Group | ||
| Screened | 323 (79.8) | 371 (74.9) |
| FIT | 69 (17.0) | 98 (19.8) |
| FIT + FLEX | 13 (3.2) | 26 (5.3) |
| Family history of breast cancer in first-degree relative | ||
| No | 316 (78.0) | 419 (84.6) |
| Yes | 81 (20.0) | 61 (12.3) |
| Missing | 8 (2.0) | 15 (3.0) |
| BMI | ||
| <25.0 | 147 (36.3) | 210 (42.4) |
| 25.0-29.9 | 138 (34.1) | 156 (31.5) |
| >30.0 | 116 (28.6) | 125 (25.3) |
| Missing | 4 (1.0) | 4 (0.8) |
| Alcohol use in the last month | ||
| No | 164 (40.5) | 207 (41.8) |
| Yes | 241 (59.5) | 288 (58.2) |
| Parity | ||
| Nulliparous | 51 (12.6) | 46 (9.3) |
| 1 | 47 (11.6) | 60 (12.1) |
| ≥2 | 306 (75.6) | 389 (78.6) |
| Missing | 1 (0.2) | 0 |
| Oral contraceptive use | ||
| Never | 237 (58.5) | 240 (48.5) |
| Ever | 60 (14.8) | 68 (13.7) |
| Missing | 108 (26.7) | 187 (37.8) |
| Duration of prior estrogen and/or progestin menopausal hormone therapy use, y | ||
| Never or <1 | 296 (73.1) | 378 (76.4) |
| 1-4 | 61 (15.1) | 65 (13.1) |
| 5-9 | 19 (4.7) | 27 (5.5) |
| ≥10 | 26 (6.4) | 24 (4.9) |
| Missing | 3 (0.7) | 1 (0.2) |
| Quintile of circulating estradiol, pg/mL | ||
| Q1 (<6.30) | 48 (11.9) | 99 (20.0) |
| Q2 (6.30-8.61) | 80 (19.8) | 99 (20.0) |
| Q3 (8.62-12.64) | 86 (21.2) | 99 (20.0) |
| Q4 (12.65-18.70) | 86 (21.2) | 99 (20.0) |
| Q5 (>18.70) | 105 (25.9) | 99 (20.0) |
Abbreviations: B ~ FIT, Breast and Bone Follow-up to the Fracture Intervention Trial; BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); FIT, Fracture Intervention Trial; FLEX, FIT Long-term Extension Trial.
SI conversion factor: To convert estradiol level to picomoles per liter, multiply by 3.671.