Reproductive factors in relation to breast cancer subtypesa
ER+/PR+ | ER+/PR− | ER−/PR− | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Cases | Person- years | HR | 95% CI | Cases | Person- years | HR | 95% CI | Cases | Person- years | HR | 95% CI | |
Number of births | ||||||||||||
0 | 110 | 212,629 | 1.00 | Reference | 29 | 212,495 | 1.00 | Reference | 56 | 212,539 | 1.00 | Reference |
1 | 112 | 161,964 | 0.77 | 0.56–1.04 | 35 | 161,835 | 0.86 | 0.48–1.53 | 64 | 161,887 | 1.04 | 0.69–1.56 |
2 | 136 | 171,818 | 0.76 | 0.57–1.01 | 35 | 171,649 | 0.70 | 0.40–1.22 | 107 | 171,771 | 1.54 | 1.07–2.21 |
≥3 | 99 | 144,765 | 0.53 | 0.39–0.73 | 32 | 144,649 | 0.62 | 0.35–1.11 | 89 | 144,749 | 1.48 | 0.98–1.84 |
Ptrend = 0.0002 | Ptrend = 0.08 | Ptrend = 0.009 | ||||||||||
Age at first birth | ||||||||||||
<20 | 103 | 150,943 | 1.00 | Reference | 26 | 150,808 | 1.00 | Reference | 82 | 150,906 | 1.00 | Reference |
20–24 | 106 | 162,425 | 0.90 | 0.68–1.19 | 35 | 162,306 | 1.21 | 0.72–2.04 | 82 | 162,387 | 0.97 | 0.71–1.33 |
25–29 | 80 | 100,093 | 1.23 | 0.90–1.68 | 25 | 100,004 | 1.54 | 0.85–2.79 | 59 | 100,064 | 1.32 | 0.92–1.90 |
≥30 | 58 | 65,086 | 1.34 | 0.93–1.94 | 16 | 65,016 | 1.45 | 0.72–2.94 | 37 | 65,050 | 1.47 | 0.94–2.29 |
Ptrend = 0.05 | Ptrend = 0.18 | Ptrend = 0.04 | ||||||||||
Years since last birth | ||||||||||||
≥15 | 264 | 278,425 | 1.00 | Reference | 85 | 278,121 | 1.00 | Reference | 184 | 278,295 | 1.00 | Reference |
10–14 | 26 | 65,208 | 0.93 | 0.60–1.57 | 8 | 65,179 | 0.96 | 0.42–2.21 | 29 | 57,214 | 1.30 | 0.82–2.08 |
<10 | 51 | 128,913 | 1.69 | 1.08–2.63 | 9 | 128,121 | 0.89 | 0.34–2.34 | 44 | 128,901 | 1.61 | 0.97–2.68 |
Ptrend = 0.03 | Ptrend = 0.82 | Ptrend = 0.08 | ||||||||||
Lactation, parous women only | ||||||||||||
No | 192 | 269,725 | 1.00 | Reference | 56 | 269,493 | 1.00 | Reference | 162 | 269,675 | 1.00 | Reference |
Yes | 151 | 203,135 | 1.13 | 0.91–1.42 | 46 | 202,960 | 1.25 | 0.83–1.89 | 95 | 203,047 | 0.78 | 0.60–1.03 |
<6 mo | 85 | 112,008 | 1.11 | 0.86–1.44 | 27 | 111,912 | 1.30 | 0.81–2.08 | 51 | 111,956 | 0.78 | 0.56–1.08 |
≥6 mo | 66 | 91,127 | 1.17 | 0.87–1.57 | 19 | 91,048 | 1.18 | 0.68–2.06 | 44 | 91,091 | 0.79 | 0.56–1.13 |
NOTE: HRs were derived from models that adjusted for age, time, geographic region, age at menarche, age at menopause, use of menopausal hormone supplements, use of oral contraceptives, body mass index, physical activity, alcohol intake, cigarette smoking, family history of breast cancer, and each of the other reproductive factors.
a18 breast cancer cases were classified as ER−/PR+ and were omitted from this table.