Table 3.
Case-only interaction risk ratios (IRRs) and 95% confidence intervals (CI) comparing BRCA1+ or BRCA2+ breast cancer cases to BRCA- breast cancer cases.
| BRCA1+ | BRCA2+ | BRCA− | BRCA1+ vs BRCA− | BRCA2+ vs. BRCA− | |||
|---|---|---|---|---|---|---|---|
| N (%) | N (%) | N (%) | IRR* | (95% CI) | IRR* | (95% CI) | |
| Age at menarche (years) | |||||||
| <11 | 57 (20.7) | 35 (17.6) | 182 (20.6) | 1.00 | Reference | 1.00 | Reference |
| 12–13 | 156 (56.7) | 98 (49.2) | 497 (56.2) | 0.98 | (0.69–1.39) | 1.02 | (0.67–1.56) |
| ≥14 | 62 (22.6) | 66 (33.2) | 205 (23.2) | 0.95 | (0.63–1.44) | 1.65 | (1.04–2.61) |
| Missing | 8 | 5 | 10 | ||||
| Full-term pregnancies | |||||||
| None | 81 (28.8) | 48 (23.5) | 281 (31.6) | 1.00 | Reference | 1.00 | Reference |
| 1 | 41 (14.6) | 35 (17.2) | 133 (15.0) | 1.09 | (0.71–1.68) | 1.55 | (0.95–2.52) |
| 2 | 96 (34.2) | 78 (38.2) | 299 (33.7) | 1.28 | (0.91–1.81) | 1.54 | (1.03–2.32) |
| ≥3 | 63 (22.4) | 43 (21.1) | 175 (19.7) | 1.54 | (1.04–2.28) | 1.46 | (0.90–2.35) |
| Missing | 2 | 0 | 6 | ||||
| Age at first full-term pregnancy | |||||||
| <20 years | 19 (9.6) | 15 (9.8) | 50 (8.3) | 1.00 | Reference | 1.00 | Reference |
| 20–24 years | 62 (31.5) | 42 (27.4) | 164 (27.3) | 1.03 | (0.56–1.90) | 0.86 | (0.44–1.67) |
| 25–29 years | 63 (32.0) | 41 (26.8) | 185 (30.7) | 0.83 | (0.45–1.53) | 0.73 | (0.37–1.43) |
| ≥30 years | 53 (26.9) | 55 (36.0) | 203 (33.7) | 0.63 | (0.34–1.17) | 0.90 | (0.46–1.74) |
| Missing | 3 | 3 | 5 | ||||
| Oral contraceptive use | |||||||
| Never | 47 (17.7) | 24 (12.2) | 120 (14.4) | 1.00 | Reference | 1.00 | Reference |
| Ever | 219 (82.3) | 173 (87.8) | 716 (85.7) | 0.70 | (0.48–1.02) | 1.19 | (0.74–1.91) |
| Missing | 17 | 7 | 58 | ||||
| Oral contraceptive duration | |||||||
| <12 months | 66 (26.4) | 40 (21.4) | 187 (23.9) | 1.00 | Reference | 1.00 | Reference |
| 12–35 months | 26 (10.4) | 29 (15.5) | 102 (13.0) | 0.69 | (0.41–1.15) | 1.30 | (0.76–2.22) |
| 36–59 months | 27 (10.8) | 10 (5.4) | 75 (9.6) | 0.95 | (0.56–1.61) | 0.60 | (0.28–1.27) |
| ≥60 months | 131 (52.4) | 108 (57.8) | 418 (53.5) | 0.81 | (0.57–1.15) | 1.13 | (0.74–1.71) |
| Missing duration (among users) | 16 | 10 | 54 | ||||
| Breastfeeding | |||||||
| Never | 32 (20.0) | 30 (22.3) | 97 (19.4) | 1.00 | Reference | 1.00 | Reference |
| Ever | 128 (80.0) | 101 (77.7) | 402 (80.6) | 0.88 | (0.56–1.39) | 0.76 | (0.47–1.23) |
| Missing | 40 | 25 | 108 | ||||
| BMI (kg/m2) 1 year before diagnosis | |||||||
| <25 | 98 (54.1) | 72 (53.0) | 309 (55.8) | 1.00 | Reference | 1.00 | Reference |
| ≥25 to <30 | 42 (23.2) | 38 (27.9) | 147 (26.5) | 0.99 | (0.65–1.51) | 1.09 | (0.70–1.70) |
| ≥30 | 41 (22.7) | 26 (19.1) | 98 (17.7) | 1.38 | (0.89–2.13) | 1.15 | (0.69–1.90) |
| Missing | 102 | 68 | 340 | ||||
| BMI (kg/m2) at age 18 | |||||||
| <25 | 138 (72.2) | 109 (75.7) | 413 (70.2) | 1.00 | Reference | 1.00 | Reference |
| ≥25 to <30 | 29 (15.2) | 25 (17.4) | 120 (20.4) | 0.76 | (0.48–1.20) | 0.81 | (0.50–1.31) |
| ≥30 | 24 (12.6) | 10 (6.9) | 55 (9.4) | 1.15 | (0.68–1.94) | 0.68 | (0.33–1.38) |
| Missing | 92 | 60 | 306 | ||||
| Alcohol use | |||||||
| No | 74 (28.0) | 49 (25.1) | 173 (20.9) | 1.00 | Reference | 1.00 | Reference |
| Yes | 190 (72.0) | 146 (74.9) | 656 (79.1) | 0.65 | (0.48–0.90) | 0.80 | (0.55–1.16) |
| Missing | 19 | 9 | 65 | ||||
| Smoking (Ever) | |||||||
| No | 175 (62.5) | 111 (55.0) | 514 (58.3) | 1.00 | Reference | 1.00 | Reference |
| Yes | 105 (37.5) | 91 (45.0) | 367 (41.7) | 0.87 | (0.66–1.15) | 1.14 | (0.84–1.56) |
| Missing | 3 | 2 | 13 | ||||
*
Adjusted for age and center.