| Total | Cases (all breast cancer) | Controls | P value | |||
---|---|---|---|---|---|---|---|
 | Number | Percentage | Number | Percentage | Number | Percentage |  |
Total | 28,104 | 100.0 | 575 | 100.0 | 27,529 | 100.0 | Â |
Age at menarche, years | Â | Â | Â | Â | Â | Â | Â |
   ≥ 14 | 18,237 | 64.9 | 324 | 56.3 | 17,913 | 65.1 | < 0.001 |
   12-13 | 8,952 | 31.9 | 213 | 37.0 | 8,739 | 31.7 |  |
   < 12 | 915 | 3.3 | 38 | 6.6 | 877 | 3.2 |  |
Any breast biopsy Age at screening: ≥50 years |  |  |  |  |  |  |  |
   No | 26,631 | 94.8 | 514 | 89.4 | 26,117 | 94.9 | < 0.001 |
   Yes | 1,473 | 5.2 | 61 | 10.6 | 1,412 | 5.1 |  |
Number of affected first-degree relatives Age at first live birth: < 20 years | Â | Â | Â | Â | Â | Â | Â |
   0 | 4,753 | 16.9 | 68 | 11.8 | 4,685 | 17.0 | < 0.001b |
   1 | 89 | 0.3 | 3 | 0.5 | 86 | 0.3 |  |
   > 1 | 1 | 0.0 | 0 | 0.0 | 1 | 0.0 |  |
Number of affected first-degree relatives Age at first live birth: 20-24 years | Â | Â | Â | Â | Â | Â | Â |
   0 | 10,321 | 36.7 | 149 | 26.3 | 10,172 | 37.0 |  |
   1 | 216 | 0.8 | 13 | 2.1 | 203 | 0.7 |  |
   > 1 | 6 | 0.0 | 2 | 0.3 | 4 | 0.0 |  |
Number of affected first-degree relatives Age at first live birth: 25-29 years or nulliparous | Â | Â | Â | Â | Â | Â | Â |
   0 | 9,246 | 32.9 | 230 | 40.0 | 9,016 | 32.8 |  |
   1 | 303 | 1.1 | 17 | 3.0 | 286 | 1.0 |  |
   > 1 | 4 | 0.0 | 0 | 0.0 | 4 | 0.0 |  |
Number of affected first-degree relatives Age at first live birth: > 30 years | Â | Â | Â | Â | Â | Â | Â |
   0 | 3,059 | 10.9 | 85 | 14.8 | 2,974 | 10.8 |  |
   1 | 105 | 0.4 | 7 | 1.2 | 98 | 0.4 |  |
   > 1 | 1 | 0.0 | 1 | 0.2 | 0 | 0.0 |  |