Table 1.
Breast cancer risk factors in the cohort
| Question | Group | No breast cancer | Breast cancer | OR (95 % CI) | Univariate summarya | Age-adjusted summarya |
|---|---|---|---|---|---|---|
| Age, yr | <52 | 10,601 (21 %) | 123 (18 %) | 0.85 (0.69–1.04) | 58 (52–64) | |
| 52–64 | 28,466 (57 %) | 387 (56 %) | 1.00 (reference) | 1.30 (1.14–1.48) | ||
| >64 | 10,864 (22 %) | 187 (27 %) | 1.27 (1.06–1.51) | 15.9 (P < 0.001) | ||
| Age at menarche, yr | <12 | 11,298 (23 %) | 168 (24 %) | 1.09 (0.89–1.31) | 13 (12–14) | |
| 12–13 | 20,817 (42 %) | 285 (41 %) | 1.00 (reference) | 0.99 (0.90–1.08) | 0.99 (0.90–1.08) | |
| 14+ | 16,685 (33 %) | 230 (33 %) | 1.01 (0.84–1.20) | 0.1 (P = 0.78) | 0.1 (P = 0.77) | |
| Missing | 1131 (2 %) | 14 (2 %) | 0.90 (0.50–1.49) | |||
| Parous | Yes | 43,578 (87 %) | 591 (85 %) | 1.00 (reference) | ||
| No | 6166 (12 %) | 103 (15 %) | 1.23 (0.99–1.51) | 1.23 (0.99–1.51) | 1.28 (1.03–1.58) | |
| Missing | 187 (0 %) | 3 (0 %) | 1.18 (0.29–3.12) | 3.6 (P = 0.059) | 5.0 (P = 0.026) | |
| Age at birth of first child, yr | <21 | 11,134 (26 %) | 139 (24 %) | 0.91 (0.74–1.11) | 24 (20–27) | |
| 21–27 | 21,791 (50 %) | 300 (51 %) | 1.00 (reference) | 1.09 (0.98–1.22) | 1.13 (1.01–1.26) | |
| >27 | 10,502 (24 %) | 150 (25 %) | 1.04 (0.85–1.26) | 2.4 (P = 0.12) | 4.4 (P = 0.037) | |
| Missing | 151 (0 %) | 2 (0 %) | 0.96 (0.16–3.03) | |||
| Age at menopause, yr | <46 | 16,201 (47 %) | 242 (47 %) | 0.73 (0.56–0.93) | 50 (45–51) | |
| 46–52 | 7933 (23 %) | 86 (17 %) | 1.00 (reference) | 1.30 (1.16–1.46) | 1.28 (1.14–1.44) | |
| >52 | 4906 (14 %) | 90 (18 %) | 1.23 (0.96–1.56) | 21.4 (P < 0.001) | 18.4 (P < 0.001) | |
| Missing | 5321 (15 %) | 95 (19 %) | 1.20 (0.94–1.51) | |||
| BMI, kg/m2 | <25 | 17,538 (35 %) | 216 (31 %) | 1.00 (reference) | 26.5 (23.7–30.4) | |
| 25–30 | 16,633 (33 %) | 241 (35 %) | 1.18 (0.98–1.42) | 1.10 (1.01–1.21) | 1.11 (1.01–1.21) | |
| 30+ | 12,442 (25 %) | 192 (28 %) | 1.25 (1.03–1.52) | 4.6 (P = 0.033) | 4.8 (P = 0.028) | |
| Missing | 3318 (7 %) | 48 (7 %) | 1.17 (0.85–1.59) | |||
| BMI premenopause, kg/m2 | <25 | 1710 (38 %) | 18 (31 %) | 1.00 (reference) | 26.2 (23.3–30.1) | |
| 25–30 | 1394 (31 %) | 24 (41 %) | 1.64 (0.89–3.07) | 0.98 (0.71–1.33) | 0.98 (0.70–1.32) | |
| 30+ | 1087 (24 %) | 14 (24 %) | 1.22 (0.60–2.46) | 0.0 (P = 0.92) | 0.0 (P = 0.88) | |
| Missing | 322 (7 %) | 3 (5 %) | 0.89 (0.21–2.63) | |||
| BMI perimenopause, kg/m2 | <25 | 3176 (36 %) | 33 (34 %) | 1.00 (reference) | 26.4 (23.5–30.3) | |
| 25–30 | 2816 (32 %) | 33 (34 %) | 1.13 (0.69–1.84) | 1.00 (0.77–1.27) | 1.00 (0.77–1.27) | |
| 30+ | 2151 (25 %) | 25 (26 %) | 1.12 (0.66–1.88) | 0.0 (P = 0.99) | 0.0 (P = 0.99) | |
| Missing | 601 (7 %) | 7 (7 %) | 1.12 (0.45–2.40) | |||
| BMI postmenopause, kg/m2 | <25 | 11,918 (35 %) | 157 (31 %) | 1.00 (reference) | 26.5 (23.8–30.4) | |
| 25–30 | 11,767 (34 %) | 176 (34 %) | 1.14 (0.91–1.41) | 1.13 (1.02–1.25) | 1.14 (1.02–1.26) | |
| 30+ | 8603 (25 %) | 144 (28 %) | 1.27 (1.01–1.60) | 5.2 (P =0.023) | 5.5 (P = 0.019) | |
| Missing | 2073 (6 %) | 36 (7 %) | 1.32 (0.90–1.88) | |||
| First-degree relatives with breast cancer | 0 | 44,269 (89 %) | 595 (85 %) | 1.00 (reference) | ||
| 1 | 5257 (11 %) | 92 (13 %) | 1.30 (1.04–1.62) | 1.32 (1.09–1.58) | 1.30 (1.07–1.56) | |
| 2+ | 405 (1 %) | 10 (1 %) | 1.84 (0.91–3.27) | 7.8 (P =0.005) | 7.0 (P = 0.008) | |
| Biopsies | No | 41,311 (83 %) | 530 (76 %) | 1.00 (reference) | ||
| Yes | 7174 (14 %) | 136 (20 %) | 1.48 (1.22–1.78) | 1.48 (1.22–1.78) | 1.45 (1.19–1.75) | |
| Missing | 14,46 (3 %) | 31 (4 %) | 1.67 (1.14–2.37) | 15.0 (P < 0.001) | 13.6 (P <0.001) | |
| Current HRT by age group, yr, yes/no | <58, no | 23,758 (48 %) | 286 (41 %) | 1.00 (reference) | ||
| <58, yes | 2529 (5 %) | 29 (4 %) | 0.95 (0.64–1.37) | 1.12 (0.82–1.49) | 1.43 (1.03–1.95) | |
| 58+, no | 22,328 (45 %) | 354 (51 %) | 1.32 (1.13–1.54) | 0.5 (P = 0.47) | 4.7 (P = 0.031) | |
| 58+, yes | 1316 (3 %) | 28 (4 %) | 1.77 (1.17–2.57) |
HRT hormone replacement therapy, BMI body mass index, OR odds ratio, CI confidence interval
aSummary, first row: median [interquartile rage (IQR)], second row: IQR odds ratio (95 % confidence interval), third row: likelihood ratio χ2 (P-value)