Table 2.
Baseline characteristics of study population matched by age, date of mammogram, and study
| Cases | Controls | |
|---|---|---|
| N | 1171 | 1659 |
| Mean age at mammogram (years) | 55.4 (10.6) | 55.3 (10.6) |
| Mean age at diagnosis (years) | 60.5 (10.8) | – |
| Mean BMI (kg/m2) | 25.7 (6.1) | 25.8 (6.8) |
| Body mass index categories (kg/m2)* | ||
| < 25 | 551 (47.1%) | 854 (51.5%) |
| 25–29 | 369 (31.5%) | 443 (26.7%) |
| 30–34 | 155 (13.2%) | 196 (11.8%) |
| 35+ | 73 (6.2%) | 136 (8.2%) |
| Unknown | 23 (2.0%) | 30 (1.8%) |
| Menopausal Status | ||
| Premenopausal | 430 (36.7%) | 632 (38.1%) |
| Postmenopausal | 697 (59.5%) | 962 (58%) |
| Unknown | 44 (3.8%) | 65 (3.9%) |
| Parity | ||
| Nulliparous | 169 (14.4%) | 218 (13.1%) |
| Parous | 977 (83.4%) | 1415 (85.3%) |
| Unknown | 25 (2.1%) | 26 (1.6%) |
| Postmenopausal hormone therapya* | ||
| Not current | 255 (51.5%) | 367 (57.5%) |
| Current, estrogen | 116 (23.4%) | 156 (24.5%) |
| Current, estrogen + progestin | 124 (25.1%) | 115 (18.0%) |
| Family history* | ||
| No | 973 (83.1%) | 1453 (87.6%) |
| Yes | 196 (16.7%) | 206 (12.4%) |
| Unknown | 2 (0.2%) | 0 (0%) |
| Standardized mean percent mammographic density (%)* | 32.9 (18.7) | 27.9 (18.4) |
| Standardized mean dense area (cm2)* | 63.5 (43.1) | 52.2 (37.8) |
| Standardized mean non-dense area (cm2)* | 149.4 (98.7) | 158.9 (102.1) |
Data are presented as the mean (standard deviation) or number (%).
aAmong postmenopausal women in MMHS, NHS, NHSII, and SFMR
*p < 0.05, cases versus controls
BMI body mass index