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Table 2 Reproductive factors and risk of ER+PR+ and ER-PR- breast cancer in all women

From: Reproductive factors and risk of hormone receptor positive and negative breast cancer: a cohort study

  Age and center stratified Multivariable adjusted1
  ER+PR+ ER-PR- ER+PR+ ER-PR-
(n = 3567) (n = 998) (n = 3567) (n = 998)
Reproductive factor Cases HR 95% CI Cases HR 95% CI Cases HR 95% CI Cases HR 95% CI
Age at menarche
<13 years 1373 1.00 Reference 376 1.00 Reference 1373 1.00 Reference 376 1.00 Reference
14 years 1717 0.96 (0.90-1.04) 481 0.98 (0.86-1.13) 1717 0.96 (0.89-1.03) 481 0.97 (0.85-1.12)
≥15 years 439 0.76 (0.68-0.85) 135 0.85 (0.69-1.04) 439 0.76 (0.68-0.85) 135 0.84 (0.69-1.03)
P for trend    <0.001    0.17    <0.001    0.17
Subtype heterogeneity2       0.44       0.48
Age at menopause 3
≤48 years 464 1.00 Reference 135 1.00 Reference 464 1.00 Reference 135 1.00 Reference
49–50 years 397 1.10 (0.95-1.26) 116 1.09 (0.84-1.41) 397 1.12 (0.98-1.29) 116 1.09 (0.84-1.42)
51–54 years 280 1.04 (0.89-1.21) 63 0.88 (0.64-1.20) 280 1.06 (0.91-1.24) 63 0.87 (0.64-1.20)
≥55 years 121 1.19 (0.97-1.47) 32 1.06 (0.71-1.58) 121 1.17 (0.95-1.44) 32 1.03 (0.69-1.54)
P for trend    0.18    0.79    0.18    0.79
Subtype heterogeneity2       0.40       0.34
Ever a full-term birth
No 446 1.00 Reference 115 1.00 Reference 446 1.00 Reference 115 1.00 Reference
Yes 2994 0.86 (0.77-0.95) 843 0.97 (0.80-1.19) 2994 0.87 (0.78-0.96) 843 0.98 (0.80-1.20)
P for significance    0.003    0.78    0.01    0.78
Subtype heterogeneity2       0.92       0.88
Number of full-term childbirths 4
1 child 612 1.00 Reference 160 1.00 Reference 612 1.00 Reference 160 1.00 Reference
2 children 1497 0.92 (0.84-1.01) 432 1.02 (0.85-1.22) 1497 0.92 (0.84-1.01) 432 1.01 (0.84-1.22)
>3 children 840 0.77 (0.69-0.85) 244 0.89 (0.72-1.09) 840 0.76 (0.68-0.85) 244 0.89 (0.73-1.10)
P for trend    <0.001    0.19    <0.001    0.19
Subtype heterogeneity2       0.22       0.20
Age at first full-term childbirth 4
≤19 years 357 1.00 Reference 103 1.00 Reference 357 1.00 Reference 103 1.00 Reference
20–24 years 1369 1.06 (0.94-1.20) 431 1.20 (0.97-1.50) 1369 1.07 (0.95-1.21) 431 1.20 (0.96-1.50)
25–29 years 912 1.20 (1.06-1.36) 242 1.16 (0.92-1.47) 912 1.22 (1.07-1.39) 242 1.17 (0.92-1.50)
30–34 years 275 1.35 (1.15-1.59) 61 1.10 (0.80-1.52) 275 1.39 (1.18-1.64) 61 1.12 (0.81-1.56)
≤35 years 82 1.44 (1.13-1.83) 14 0.91 (0.52-1.60) 82 1.47 (1.15-1.88) 14 0.93 (0.53-1.65)
P for trend    <0.001    0.96    <0.001    0.96
Subtype heterogeneity2       0.02       0.03
Time between menarche and first full-term childbirth 4
<10 years 837 1.00 Reference 257 1.00 Reference 837 1.00 Reference 257 1.00 Reference
≥10 years 2133 1.21 (1.12-1.31) 592 1.14 (0.98-1.32) 2133 1.22 (1.12-1.33) 592 1.15 (0.99-1.34)
P for significance    <0.001    0.09    <0.001    0.09
Subtype heterogeneity2       0.49       0.52
Age at last full-term childbirth 4
≤24 years 463 1.00 Reference 138 1.00 Reference 463 1.00 Reference 138 1.00 Reference
25–29 years 1058 0.98 (0.88-1.10) 321 1.01 (0.82-1.23) 1058 0.98 (0.88-1.10) 321 1.01 (0.82-1.23)
30–34 years 984 1.07 (0.95-1.20) 263 0.97 (0.78-1.19) 984 1.07 (0.96-1.20) 263 0.98 (0.79-1.21)
≥35 years 490 1.11 (0.97-1.26) 130 1.01 (0.79-1.29) 490 1.12 (0.98-1.28) 130 1.03 (0.80-1.33)
P for trend    0.03    0.90    0.02    0.90
Subtype heterogeneity2       0.24       0.29
Time since last full-term childbirth 4
≤20 years 1043 1.00 Reference 300 1.00 Reference 1043 1.00 Reference 300 1.00 Reference
>20 years 1952 0.87 (0.78-0.96) 552 1.00 (0.82-1.22) 1952 0.86 (0.77-0.95) 552 0.98 (0.81-1.20)
P for significance    0.01    0.98    0.01    0.98
Subtype heterogeneity2       0.20       0.24
Ever breast-fed 4
No 538 1.00 Reference 152 1.00 Reference 538 1.00 Reference 152 1.00 Reference
Yes 2317 0.99 (0.90-1.09) 642 0.97 (0.81-1.16) 2317 0.99 (0.89-1.09) 642 0.98 (0.81-1.17)
P for significance    0.82    0.74    0.76    0.74
Subtype heterogeneity2       0.85       0.93
Total cumulative breastfeeding duration 4,5
<1 month 249 1.00 Reference 72 1.00 Reference 249 1.00 Reference 72 1.00 Reference
1–3 months 602 1.04 (0.89-1.20) 155 0.91 (0.69-1.21) 602 1.04 (0.89-1.20) 155 0.91 (0.69-1.21)
4–6 months 460 0.97 (0.83-1.14) 137 0.98 (0.74-1.32) 460 0.97 (0.83-1.14) 137 0.99 (0.74-1.32)
7–12 months 487 0.97 (0.83-1.13) 132 0.91 (0.68-1.22) 487 0.97 (0.83-1.13) 132 0.91 (0.68-1.23)
13–17 months 182 0.91 (0.75-1.11) 62 1.10 (0.78-1.57) 182 0.92 (0.75-1.12) 62 1.12 (0.79-1.60)
≥18 months 293 1.09 (0.91-1.31) 77 1.04 (0.73-1.46) 293 1.11 (0.92-1.33) 77 1.07 (0.75-1.51)
P for trend    0.99    0.54    0.90    0.54
Subtype heterogeneity2       0.58       0.53
Ever an abortion 6
No 1552 1.00 Reference 435 1.00 Reference 1552 1.00 Reference 435 1.00 Reference
Yes 1016 1.00 (0.92-1.08) 293 1.00 (0.86-1.16) 1016 0.99 (0.91-1.07) 293 1.00 (0.86-1.16)
P for significance    0.97    0.98    0.72    0.98
Subtype heterogeneity2       0.97       0.86
OC use at recruitment
Never OC user 1477 1.00 Reference 379 1.00 Reference 1477 1.00 Reference 379 1.00 Reference
Past OC user 1839 1.00 (0.93-1.08) 548 1.11 (0.96-1.28) 1839 0.97 (0.90-1.05) 548 1.09 (0.94-1.26)
Current OC user 108 1.20 (0.97-1.47) 33 1.08 (0.73-1.59) 108 1.19 (0.96-1.47) 33 1.09 (0.74-1.63)
P for trend    0.42    0.20    0.95    0.20
Subtype heterogeneity7       0.34       0.30
Age started OC 8
≤24 years 899 1.00 Reference 292 1.00 Reference 899 1.00 Reference 292 1.00 Reference
25–29 years 335 0.86 (0.75-0.99) 94 0.86 (0.66-1.11) 335 0.87 (0.76-1.00) 94 0.86 (0.66-1.11)
30–34 years 303 0.91 (0.78-1.07) 90 0.92 (0.69-1.23) 303 0.93 (0.79-1.08) 90 0.92 (0.69-1.22)
≥35 years 265 1.07 (0.90-1.28) 73 0.97 (0.70-1.36) 265 1.09 (0.91-1.30) 73 0.97 (0.70-1.36)
P for trend    0.83    0.75    0.67    0.75
Subtype heterogeneity2       0.70       0.61
Duration of OC use 8
1 year or less 396 1.00 Reference 114 1.00 Reference 396 1.00 Reference 114 1.00 Reference
2–4 years 450 1.02 (0.89-1.17) 116 0.86 (0.66-1.12) 450 1.03 (0.89-1.18) 116 0.86 (0.67-1.12)
5–9 years 426 1.06 (0.92-1.22) 122 0.97 (0.75-1.26) 426 1.06 (0.92-1.22) 122 0.97 (0.75-1.27)
≥10 years 521 1.02 (0.89-1.17) 187 1.11 (0.87-1.41) 521 1.02 (0.89-1.18) 187 1.11 (0.87-1.42)
P for trend    0.70    0.21    0.68    0.21
Subtype heterogeneity2       0.36       0.37
  1. 1Stratified by age at recruitment and center and further adjusted for BMI, height, menopausal status at enrolment, HRT use, physical activity, smoking status, alcohol consumption and attained level of education; 2heterogeneity between ER+PR+ and ER-PR- tumors was assessed on the trend score using the data augmentation method as described by Lunn and McNeil; 3in postmenopausal women only; 4in parous women only; 5in women who breast-fed only; 6in both spontaneous and induced abortions; 7heterogeneity between ER+PR+ and ER-PR- tumors was assessed on the unordered categorical variable of never, past and current OC use using the data augmentation method as described by Lunn and McNeil; 8in women who ever used OC.
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