TABLE 2.
Multivariate-adjusted odds ratios for reproductive and hormonal factors by tumor subtype*
| Reproductive/hormonal characteristic |
Controls n (%) |
Luminal | HER2-overexpressing | Triple-negative | |||
|---|---|---|---|---|---|---|---|
| n (%) | OR (95% CI) | n (%) | OR (95% CI) | n (%) | OR (95% CI) | ||
| Age at menarche | |||||||
| ≥13 | 817 (55) | 552 (54) | 1.0 (ref) | 12 (31) | 1.0 (ref) | 41 (53) | 1.0 (ref) |
| <13 | 658 (45) | 467 (46) | 1.0 (0.9-1.2) | 27 (69) | 2.7 (1.4-5.5)†‡ | 37 (47) | 1.1 (0.7-1.7) |
| Parity | |||||||
| Nulliparous | 130 (9) | 114 (11) | 1.0 (ref) | 3 (8) | 1.0 (ref) | 7 (9) | 1.0 (ref) |
| Parous | 1346 (91) | 909 (89) | 0.8 (0.6-1.0) | 36 (92) | 1.2 (0.4-3.9) | 71 (91) | 1.1 (0.5-2.3) |
| Number of live births§ | |||||||
| 1 | 117 (9) | 96 (11) | 1.0 (ref) | 4 (11) | 1.0 (ref) | 9 (13) | 1.0 (ref) |
| 2 | 352 (26) | 270 (30) | 1.0 (0.7-1.3) | 16 (44) | 1.1 (0.4-3.5) | 21 (30) | 0.8 (0.3-1.7) |
| ≥3 | 877 (65) | 543 (60) | 0.8 (0.6-1.1) | 16 (44) | 0.4 (0.1-1.3) | 41 (58) | 0.8 (0.3-1.7) |
| Age at 1st live birth§ | |||||||
| <20 | 274 (20) | 178 (20) | 1.0 (ref) | 4 (11) | 1.0 (ref) | 14 (18) | 1.0 (ref) |
| 20-24 | 651 (48) | 435 (48) | 1.0 (0.8-1.3) | 24 (67) | 2.3 (0.8-6.8) | 34 (49) | 1.1 (0.6-2.1) |
| 25-29 | 305 (23) | 200 (22) | 1.0 (0.7-1.3) | 6 (17) | 1.0 (0.3-3.8) | 19 (27) | 1.3 (0.6-2.8) |
| ≥30 | 113 (8) | 93 (10) | 1.2 (0.8-1.7) | 2 (6) | 0.7 (0.1-4.4) | 4 (6) | 0.7 (0.2-2.3) |
| Breastfeeding history§ | |||||||
| Never | 471 (35) | 374 (41) | 1.0 (ref) | 12 (33) | 1.0 (ref) | 31 (44) | 1.0 (ref) |
| Ever for <6 months | 408 (30) | 249 (27) | 0.8 (0.6-0.9)† | 10 (28) | 1.0 (0.4-2.3) | 25 (35) | 0.9 (0.5-1.6) |
| Ever for ≥6 months | 467 (35) | 286 (31) | 0.8 (0.6-1.0)† | 14 (39) | 1.5 (0.7-3.3) | 15 (21) | 0.5 (0.3-0.9)† |
| Type of menopause | |||||||
| Natural | 873 (60) | 663 (66) | 1.0 (ref) | 22 (56) | 1.0 (ref) | 45 (59) | 1.0 (ref) |
| Surgical (bilateral oophorectomy) | 243 (17) | 129 (13) | 0.7 (0.6-0.9)† | 6 (15) | 1.0 (0.4-2.5) | 10 (17) | 0.8 (0.4-1.6) |
| Simple hysterectomy | 329 (23) | 208 (21) | 0.8 (0.7-1.0) | 11 (28) | 1.3 (0.6-2.8) | 21 (28) | 1.3 (0.7-2.1) |
| Age at menopause¶,** | |||||||
| <45 | 250 (23) | 117 (15) | 1.0 (ref) | 4 (15) | 1.0 (ref) | 11 (20) | 1.0 (ref) |
| 45-54 | 668 (61) | 502 (66) | 1.4 (1.1-1.9)† | 15 (56) | 1.4 (0.4-4.6) | 32 (59) | 0.9 (0.4-2.0) |
| ≥55 | 169 (16) | 144 (19) | 1.6 (1.1-2.2)† | 8 (30) | 2.9 (0.8-10.7) | 11 (20) | 1.2 (0.5-3.0) |
| p for linear trend: | p < 0.01 | p = 0.07 | p = 0.65 | ||||
| Hormone therapy use¶ | |||||||
| Never use | 537 (37) | 343 (35) | 1.0 (ref) | 10 (26) | 1.0 (ref) | 31 (41) | 1.0 (ref) |
| Former use only | 248 (17) | 162 (16) | 1.0 (0.8-1.3) | 11 (30) | 2.2 (0.9-5.4) | 13 (17) | 0.8 (0.4-1.6) |
| Current unopposed estrogen use | 438 (30) | 242 (24) | 0.9 (0.7-1.1) | 10 (27) | 1.0 (0.4-2.6) | 21 (28) | 0.7 (0.4-1.4) |
| Current estrogen+progestin use | 215 (15) | 242 (24) | 1.7 (1.3-2.1)† | 6 (16) | 1.4 (0.5-4.2) | 10 (13) | 0.6 (0.3-1.3)‡ |
*
Odds ratios (OR) adjusted for age and diagnosis / reference year.
†
OR vs. controls p<0.05.
‡
OR vs. luminal cases p<0.05.
§
Excludes nulliparous women. Number of live births, age at first live birth, and breastfeeding are co-adjusted for each other.
¶
Additionally adjusted for type of menopause.
**
Excludes women with cessation of menses due to hysterectomy without bilateral oophorectomy.