Table 2.
Demographic characteristics and Gail model clinical risk factors for breast cancer in the nested case–control cohort*
| Characteristics | Case patients, No. (%) | Control subjects, No. (%) | Ptrend† |
| Total | 1664 (100) | 1636 (100) | |
| ER status | |||
| ER-positive tumor | 1218 (73.2) | ||
| ER-negative tumor | 208 (12.5) | ||
| Unknown‡ or missing§ | 238 (14.3) | ||
| Age at screening, y | .84 | ||
| 50–59 | 510 (30.6) | 510 (31.2) | |
| 60–69 | 789 (47.4) | 767 (46.9) | |
| 70–79 | 365 (21.9) | 359 (21.9) | |
| Missing§ | 0 (0.0) | 0 (0.0) | |
| Age at menarche, y | .02 | ||
| <12 | 379 (22.8) | 349 (21.3) | |
| 12 | 441 (26.5) | 407 (24.9) | |
| 13 | 497 (29.9) | 481 (29.4) | |
| ≥14 | 338 (20.3) | 395 (24.1) | |
| Missing§ | 9 (0.5) | 4 (0.2) | |
| Age at birth of first child, y | .004 | ||
| <20 | 182 (10.9) | 214 (13.1) | |
| 20–24 | 625 (37.6) | 665 (40.6) | |
| 25–29 | 370 (22.2) | 349 (21.3) | |
| ≥30 | 151 (9.1) | 117 (7.2) | |
| No term pregnancy | 200 (12.0) | 166 (10.1) | |
| Missing§ | 136 (8.2) | 125 (7.6) | |
| Age at menopause, y | .52 | ||
| <45 | 300 (18.0) | 294 (18.0) | |
| 45–49 | 355 (21.3) | 390 (23.8) | |
| 50–54 | 646 (38.8) | 596 (36.4) | |
| >54 | 238 (14.3) | 237 (14.5) | |
| Missing§ | 125 (7.5) | 119 (7.3) | |
| First-degree relatives with breast cancer | .0001 | ||
| 0 | 1253 (75.3) | 1319 (80.6) | |
| >1 | 309 (18.6) | 226 (13.8) | |
| Missing§ | 102 (6.1) | 91 (5.6) | |
| Number of previous breast biopsies | 1 × 10−5 | ||
| 0 | 1056 (63.5) | 1148 (70.2) | |
| 1 | 298 (17.9) | 188 (11.5) | |
| >2 | 102 (6.1) | 83 (5.1) | |
| Missing§ | 208 (12.5) | 217 (13.3) | |
*
The nested case–control cohort was selected from the Women's Health Initiative (WHI) Clinical Trial. ER = estrogen receptor.
†
Ptrend values were calculated using the two-sided Cochran–Armitage test for trend.
‡
Pathology data on tumor ER status was unavailable or indeterminate.
§
Data for the specified characteristic was not available from the WHI Clinical Trial.