Table 1 Baseline characteristics of cases and controls, and odds ratios for total breast cancer in the NBCSP case-control study
Characteristic | No. of controls (%) | No. of breast cancer cases (%) | Odds ratioa (95% CI) | P valueb |
|---|---|---|---|---|
Screening round (baseline exploration) | ||||
September 1996 to August 1998 | 3,948 (84.1) | 987 (84.1) | ||
September 1998 to August 2000 | 408 (8.7) | 102 (8.7) | ||
September 2000 to August 2002 | 224 (4.8) | 56 (4.8) | ||
September 2002 to August 2004 | 108 (2.3) | 27 (2.3) | ||
Age at baseline exploration (years) | ||||
<50 | 1,733 (37.0) | 433 (37.0) | ||
50-54 | 986 (21.0) | 245 (20.9) | ||
55-59 | 897 (19.1) | 228 (19.5) | ||
60-64 | 870 (18.6) | 217 (18.5) | ||
≥65 | 202 (4.3) | 49 (4.2) | ||
Age at menarche (years) | 0.357c | |||
≥15 | 724 (15.5) | 161 (13.7) | 0.95 (0.77-1.18) | |
14 | 1,243 (26.5) | 290 (24.7) | 1.00 (reference) | |
13 | 1,281 (27.3) | 363 (31.0) | 1.22 (1.03-1.45) | |
12 | 867 (18.5) | 225 (19.2) | 1.11 (0.92-1.35) | |
<12 | 569 (12.1) | 132 (11.3) | 1.00 (0.79-1.25) | |
Unknown | 4 (0.1) | 1 (0.1) | ||
Age at first live birth (years) | <0.001 | |||
<20 | 102 (2.2) | 13 (1.1) | 0.51 (0.28-0.91) | |
20-24 | 1,441 (30.7) | 293 (25.0) | 0.81 (0.68-0.95) | |
25-29 | 1,823 (38.9) | 457 (39.0) | 1.00 (reference) | |
30-34 | 522 (11.1) | 134 (11.4) | 1.03 (0.83-1.28) | |
≥35 | 175 (3.7) | 57 (4.9) | 1.31 (0.95-1.80) | |
Nulliparous | 625 (13.3) | 218 (18.6) | 1.41 (1.17-1.70) | |
Age at menopause (years) | 0.001 | |||
≤45 | 777 (16.6) | 147 (12.5) | 1.00 (reference) | |
46-50 | 1,244 (26.5) | 298 (25.4) | 1.25 (1.01-1.56) | |
>50 | 1,035 (22.1) | 293 (25.0) | 1.48 (1.17-1.87) | |
Premenopausal | 1,631 (34.8) | 434 (37.0) | 1.44 (1.14-1.83) | |
Unknown | 1 (0.0) | 0 (0.0) | ||
Family history of breast cancer | <0.001 | |||
None | 4,075 (86.9) | 945 (80.6) | 1.00 (reference) | |
Second-degree relative | 327 (7.0) | 109 (9.3) | 1.43 (1.14-1.80) | |
First-degree relative ≥50 years | 172 (3.7) | 64 (5.5) | 1.61 (1.19-2.16) | |
First-degree relative <50 years | 114 (2.4) | 54 (4.6) | 2.06 (1.48-2.88) | |
Previous breast biopsy | <0.001 | |||
No | 4,281 (91.3) | 1,001 (85.4) | 1.00 (reference) | |
Yes | 407 (8.7) | 171 (14.6) | 1.82 (1.50-2.22) | |
Use of hormone replacement therapy | 0.602 | |||
No | 4,208 (89.8) | 1,046 (89.2) | 1.00 (reference) | |
Yes | 480 (10.2) | 126 (10.8) | 1.06 (0.86-1.31) | |
Mammographic density (%) | <0.001c | |||
0-10 | 1,711 (36.5) | 263 (22.4) | 1.00 (reference) | |
11-25 | 1,136 (24.3) | 244 (20.8) | 1.52 (1.25-1.85) | |
26-50 | 1,158 (24.8) | 375 (32.0) | 2.47 (2.05-2.98) | |
51-75 | 529 (11.3) | 215 (18.3) | 3.27 (2.62-4.09) | |
>75 | 135 (2.9) | 59 (5.0) | 3.74 (2.63-5.32) | |
Unknown | 19 (0.4) | 16 (1.4) |