Table 1.
Demographic and reproductive characteristics of study subjects (N=75,169) as self-reported on the date of study entry
| Characteristic | All Study Subjects | Women with a Breast Cancer Diagnosis | Breast Cancer Incidence Rate per 100,0001 | |||
|---|---|---|---|---|---|---|
| N | % | Person-Years at Risk | N | % | ||
| Mailed Surveys2 | 8,793 | 11.7 | 17,324 | 35 | 3.2 | 202 |
| In Clinic Surveys3 | 66,376 | 88.3 | 201,100 | 1,052 | 96.8 | 523 |
| Age (years) | ||||||
| 40-44 | 11,887 | 15.8 | 30,064 | 71 | 6.5 | 236 |
| 45-49 | 12,184 | 16.2 | 33,562 | 133 | 12.2 | 396 |
| 50-54 | 15,121 | 20.1 | 43,831 | 158 | 14.5 | 360 |
| 55-59 | 11,284 | 15.0 | 33,139 | 169 | 15.6 | 510 |
| 60-64 | 7,302 | 9.7 | 21,763 | 140 | 12.9 | 643 |
| 65-69 | 5,293 | 7.0 | 16,654 | 125 | 11.5 | 751 |
| 70-74 | 4,557 | 6.1 | 14,735 | 108 | 9.9 | 733 |
| 75-80 | 3,808 | 5.1 | 12,357 | 92 | 8.5 | 745 |
| 80+ | 3,733 | 5.0 | 12,318 | 91 | 8.4 | 739 |
| Race | ||||||
| White | 62,475 | 83.5 | 184,465 | 949 | 87.7 | 514 |
| Black | 2,644 | 3.5 | 7,177 | 27 | 2.5 | 376 |
| American Indian | 3,124 | 4.2 | 8,983 | 43 | 4.0 | 479 |
| Asian | 5,857 | 7.8 | 15,514 | 55 | 5.1 | 355 |
| Other/Mixed | 742 | 1.0 | 1,655 | 8 | 0.7 | 483 |
| Missing | 327 | -- | 630 | 5 | -- | 794 |
| Body Mass Index (kg/m2) | ||||||
| <25 | 30,911 | 42.9 | 90,324 | 434 | 41.8 | 480 |
| 25-30 | 21,161 | 29.4 | 61,733 | 328 | 31.6 | 531 |
| 30+ | 19.915 | 27.7 | 56,722 | 277 | 26.7 | 488 |
| Missing | 3,182 | -- | 9,646 | 48 | -- | 498 |
| Menopausal Status | ||||||
| Pre/Peri-Menopausal | 22,360 | 31.7 | 60,488 | 208 | 19.8 | 344 |
| Post-Menopausal | 48,219 | 68.3 | 145,428 | 844 | 80.2 | 580 |
| Missing | 4,590 | -- | 12,508 | 35 | -- | 280 |
| Age at Menarche (years) | ||||||
| ≤ 12 | 30,516 | 46.1 | 88,795 | 452 | 47.5 | 509 |
| 13 | 18,950 | 28.6 | 54,740 | 251 | 26.4 | 459 |
| 14 | 8,790 | 13.3 | 25,657 | 140 | 14.7 | 546 |
| 15+ | 7,987 | 12.1 | 22,620 | 109 | 11.5 | 482 |
| Missing | 8,926 | -- | 26,612 | 135 | -- | 507 |
| Age at 1st Birth (years) | ||||||
| Nulliparous | 13,206 | 17.9 | 38,379 | 166 | 15.7 | 433 |
| <20 | 11,285 | 15.3 | 32,325 | 141 | 13.3 | 436 |
| 20-24 | 23,337 | 31.6 | 68,376 | 380 | 35.8 | 556 |
| 25-29 | 14,998 | 20.3 | 43,254 | 216 | 20.4 | 499 |
| 30-34 | 7,568 | 10.3 | 22,181 | 115 | 10.8 | 518 |
| 35+ | 3,397 | 4.6 | 9,705 | 43 | 4.0 | 443 |
| Missing | 1,378 | -- | 4,205 | 26 | -- | 618 |
| Hormone Use | ||||||
| Never | 35,673 | 48.7 | 97,965 | 429 | 40.5 | 438 |
| Former | 17,565 | 23.9 | 48,993 | 248 | 23.4 | 506 |
| Current4 | 20,086 | 27.4 | 66,428 | 382 | 36.1 | 575 |
| Progestin Only | 724 | 4.0 | 2,160 | 6 | 1.7 | 278 |
| Estrogen Only | 8,090 | 43.7 | 26,207 | 118 | 32.9 | 450 |
| Estrogen + Progestin | 9,704 | 52.4 | 33,081 | 235 | 65.4 | 710 |
| Missing | 1,796 | -- | 5,039 | 28 | -- | 556 |
| Breast density | ||||||
| Almost entirely fat | 2,788 | 4.1 | 7,917 | 18 | 1.9 | 227 |
| Scattered fibroglandular tissue | 20,738 | 30.8 | 62,447 | 203 | 20.8 | 325 |
| Heterogeneously dense | 34,943 | 51.9 | 105,123 | 609 | 62.5 | 579 |
| Extremely dense | 8,919 | 13.2 | 26,880 | 145 | 14.9 | 539 |
| Missing | 7,781 | -- | 16,058 | 112 | -- | 697 |
| Benign Breast Biopsy History | ||||||
| No | 61,141 | 82.7 | 175,709 | 791 | 74.4 | 450 |
| Yes | 12,831 | 17.3 | 39,218 | 272 | 25.6 | 694 |
| Missing | 1,197 | -- | 3,497 | 24 | -- | 686 |
| Mammogram within 3 years prior to baseline | ||||||
| No | 25,658 | 34.1 | 65,237 | 336 | 30.9 | 515 |
| Yes | 49,511 | 65.9 | 153,188 | 751 | 69.1 | 490 |
1
Number of breast cancer diagnoses per 100,000 person-years
2
Baseline questionnaire completed via mail by subject at age 40 or upon enrollment in Group Health
3
Baseline questionnaire was filled out in clinic during a screening or diagnostic mammogram
4
Number of specific hormone users may not add to total current hormone users due to missing data