Table 3.
Relative risks of breast cancer in Generations Study participants based on various commonly used categorizations of family history, adjusted for other breast cancer risk factors*
| Breast cancer in familya | No. of study participants (%) | Person-years (1000) | No. of breast cancer cases | HR | 95% CI | P |
|---|---|---|---|---|---|---|
| Diagnosis of breast cancer in relative | ||||||
| No | 88,219 (85.0) | 534.5 | 1,301 | 1.00 | baseline | |
| Yes | 15,519 (15.0) | 93.4 | 432 | 1.77 | 1.58, 1.97 | <0.0001 |
| No. of relatives with breast cancer | ||||||
| 0 | 88,219 (85.0) | 534.5 | 1,301 | 1.00 | baseline | |
| 1 | 14,750 (14.2) | 88.9 | 393 | 1.72 | 1.53, 1.92 | <0.0001 |
| ≥2 | 769 (0.8) | 4.5 | 39 | 2.52 | 1.83, 3.47 | <0.0001 |
| Type of relative with breast cancer | ||||||
| Unaffected relative | 88,219 (85.0) | 534.5 | 1,301 | 1.00 | baseline | |
| Mother only | 11,940 (11.5) | 71.9 | 295 | 1.72 | 1.51, 1.95 | <0.0001 |
| Sister only | 2,730 (2.6) | 16.5 | 96 | 1.73 | 1.40, 2.13 | <0.0001 |
| Daughter only | 80 (0.1) | 0.5 | 2 | 1.22 | 0.30, 4.89 | 0.78 |
| Combination of relativesa | 769 (0.8) | 4.5 | 39 | 2.52 | 1.83, 3.47 | <0.0001 |
| Age of relative at diagnosis(years)b | ||||||
| Unaffected relative | 88,219 (85.0) | 534.5 | 1301 | 1.00 | baseline | |
| <45 | 2828 (2.8) | 16.9 | 97 | 2.47 | 2.01, 3.04 | <0.0001 |
| ≥45 | 12,691 (12.2) | 76.5 | 335 | 1.63 | 1.45, 1.84 | <0.0001 |
HR Hazard Ratio from Cox regression using age as time scale, CI Confidence Interval
*Adjusted for age at menarche, benign breast disease, oral contraceptive use, parity, age at first birth, breastfeeding, age at menopause, hormone replacement therapy use, physical activity, pre- and post-menopausal body mass index, alcohol intake, smoking status, and socioeconomic status
aFirst-degree female relatives
bYoungest if >1 relative with breast cancer