Table 1 Characteristics of breast cancer case participants and control participants
| Â | Overall | By study | ||
|---|---|---|---|---|
Women’s CARE | Women’s BCIS | Women’s LIFE | ||
Case participants | N = 2658 | N = 1197 | N = 342 | N = 1119 |
Mean age at diagnosis, years (SD, range) | 46.7 (8.1, 22-64) | 49.0 (8.6, 35-64) | 51.8 (7.3, 35-64) | 42.7 (5.4, 22-49) |
Race | ||||
 White | 1960 (73.7%) | 678 (56.6%) | 287 (83.9%) | 995 (88.9%) |
 African-American | 698 (26.3%) | 519 (43.4%) | 55 (16.1%) | 124 (11.1%) |
Subtype of breast cancer | ||||
 Triple-negative | 554 (20.8%) | 335 (28.0%) | 21 (6.1%) | 198 (17.7%) |
 Luminal A-like | 1517 (57.1%) | 645 (53.9%) | 233 (68.1%) | 639 (57.1%) |
 Luminal B-like | 360 (13.5%) | 121 (10.1%) | 49 (14.3%) | 190 (17.0%) |
 HER2-enriched | 227 (8.5%) | 96 (8.0%) | 39 (11.4%) | 92 (8.2%) |
Control participants | N = 2448 | N = 2011a | ─ | N = 437 |
Mean age at reference date, years (SD, range) | 47.8 (8.3, 24-64) | 48.9 (8.4, 35-64) | ─ | 42.6 (4.9, 24-49) |
Race | ||||
 White | 1549 (63.3%) | 1147 (57.0%) | ─ | 402 (92.0%) |
 African-American | 899 (36.7%) | 864 (43.0%) | ─ | 35 (8.0%) |
Mean age at menarche, years (SD) | 12.4 (1.6) | 12.4 (1.6) | ─ | 12.7 (1.5) |
Ever had a completed (>26-week) pregnancy | 1990 (81.3%) | 1677 (83.4%) | ─ | 313 (71.6%) |
Among parous women | N = 1990 | N = 1677 |  | N = 313 |
 Mean number of completed pregnancies (SD) | 2.7 (1.5) | 2.8 (1.6) | ─ | 2.2 (1.1) |
 Mean age at first completed pregnancy (SD) | 23.2 (5.7) | 22.5 (5.3) | ─ | 27.1 (6.2) |
 Ever breastfed | 1242 (62.4%) | 967 (57.7%) | ─ | 275 (87.9%) |
 Mean duration of breastfeeding among those who breastfed, months (SD) | 12.1 (15.0) | 10.9 (14.4) | ─ | 16.2 (16.5) |