Table 3. Relationship between reproductive factors and risk of breast cancer subtypes †.
| Luminal A | Luminal B | Triple-negative | HER2-overexpressing | ||||
|---|---|---|---|---|---|---|---|
| n (%) | n (%) | OR (95% CI) | n (%) | OR (95% CI) | n (%) | OR (95% CI) | |
|
|
|||||||
| Number of full term pregnancies | |||||||
| Nulliparous | 191 (24.7) | 39 (30.0) | 1.00 (ref) | 291 (22.6) | 1.00 (ref) | 92 (19.0) | 1.00 (ref) |
| Parous | 583 (75.3) | 91 (70.0) | 0.82 (0.54-1.24) | 994 (77.4) | 1.13 (0.91-1.39) | 392 (81.0) | 1.43 (1.08-1.89)* |
| 1 | 124 (16.0) | 26 (20.0) | 1.05 (0.61-1.82) | 234 (18.2) | 1.24 (0.93-1.65) | 83 (17.1) | 1.43 (0.98-2.08) |
| 2 | 287 (37.1) | 40 (30.8) | 0.73 (0.45-1.18) | 432 (33.6) | 1.00 (0.79-1.27) | 178 (36.8) | 1.31 (0.96-1.79) |
| ≥3 | 172 (22.2) | 25 (19.2) | 0.79 (0.46-1.37) | 328 (25.5) | 1.27 (0.98-1.66) | 131 (27.1) | 1.63 (1.16-2.29)* |
| P-value for trend (among parous women only) | 0.416 | 0.729 | 0.431 | ||||
| Age at first full-term pregnancy ‡ | |||||||
| <20 | 76 (14.0) | 14 (16.9) | 1.00 (ref) | 183 (20.1) | 1.00 (ref) | 61 (17.4) | 1.00 (ref) |
| 20-24 | 176 (32.4) | 19 (22.9) | 0.56 (0.27-1.19) | 301 (33.1) | 0.70 (0.51-0.97)* | 115 (32.8) | 0.83 (0.55-1.25) |
| 25-29 | 153 (28.1) | 25 (30.1) | 0.82 (0.40-1.69) | 230 (25.3) | 0.61 (0.43-0.86)* | 86 (24.5) | 0.70 (0.46-1.08) |
| 30+ | 139 (25.6) | 25 (30.1) | 0.84 (0.40-1.73) | 196 (21.5) | 0.56 (0.40-0.80)* | 89 (25.4) | 0.81 (0.52-1.25) |
| Continuous (1-year) | 1.01 (0.97-1.05) | 0.97 (0.95-0.99)* | 0.99 (0.97-1.01) | ||||
| P-value for trend | 0.574 | 0.003 | 0.557 | ||||
| Age at menopause § | |||||||
| <45 | 35 (10.0) | 9 (21.4) | 1.00 (ref) | 136 (23.3) | 1.00 (ref) | 43 (18.4) | 1.00 (ref) |
| 45-54 | 277 (78.9) | 29 (69.0) | 0.41 (0.17-0.97)* | 396 (67.8) | 0.41 (0.27-0.63)* | 166 (70.9) | 0.50 (0.30-0.83)* |
| 55+ | 39 (11.1) | 4 (9.5) | 0.51 (0.14-1.89) | 52 ( 8.9) | 0.39 (0.22-0.70)* | 25 (10.7) | 0.66 (0.33-1.34) |
| Continuous (1-year) | 0.97 (0.91-1.04) | 0.97 (0.94-1.00)* | 0.99 (0.96-1.03) | ||||
| P-value for trend | 0. 397 | 0.024 | 0.759 | ||||
*
Statistically significant at p<0.05.
†
Number in columns may not add up to the total number of cases due to missingness in these variables. Odds ratios were adjusted for reference year, age at reference date and study site.
‡
Restricted to women who ever had a full term pregnancy.
§
Restricted to postmenopausal women with known age at menopause.