Table 1.
Characteristics of breast cancer cases and noncases.
| Variable | Cases | Noncases |
|---|---|---|
| Entire cohort | ||
| No. of workers | 281 | 5,471 |
| Year of birth (mean ± SD) | 1926 ± 11** | 1930 ± 13 |
| Years exposed (mean ± SD) | 9.3 ± 8.2** | 7.7 ± 7.6 |
| Cumulative exposure (1,000 unit-years) | ||
| Mean ± SD | 0.67 ± 0.95 | 0.57 ± 0.93 |
| Median | 0.27* | 0.22 |
| Questionnaire subcohorta | ||
| No. of workers | 201 | 3,751 |
| Year of birth (mean ± SD) | 1928 ± 11** | 1932 ± 12 |
| Self-respondent on questionnaire (%) | 63.7** | 82.0 |
| Nonwhite ethnicity (%) | 7.5 | 9.3 |
| Ever-smoker (%) | 51.0 | 52.3 |
| BMI at 20 years of age [kg/m2 (mean ± SD)] | 20.8 ± 3.0 | 21.2 ± 3.2 |
| Age at menarche [years (mean ± SD)] | 12.8 ± 1.7 | 12.9 ± 1.7 |
| Premenopausal at diagnosis (%) | 15.4 | NA |
| Parous (%) | 86.1 | 86.7 |
| No. of live births (mean ± SD) | 2.5 ± 1.7 | 2.5 ± 1.8 |
| Age at first live birth [years (mean ± SD)] | 23.8 ± 4.2** | 23.0 ± 4.5 |
| Used hormone replacement therapy (%) | 27.5 | 33.3 |
| Age began hormone replacement use [years (mean ± SD)] | 46.5 ± 8.8 | 47.2 ± 9.2 |
| Breast cancer in first-degree female relative (%) | 21.2* | 13.9 |
| Years exposed (mean ± SD) | 8.9 ± 8.2* | 7.4 ± 7.4 |
| Cumulative exposure (1,000 unit-years) | ||
| Mean ± SD | 0.59 ± 0.84 | 0.52 ± 0.89 |
| Median | 0.27 | 0.20 |
NA, not applicable.
a
Questionnaire subcohort comprises members of the full cohort for whom some questionnaire data were available. Not all participants (or their proxies) provided responses for each question; some variables have missing values.
*
p < 0.05
**
p < 0.01.