Table 4.
Pack-years of smoking relevant to menarche, age at first birth and menopause in relation to the incidence of breast cancer among 111,140 participants of NHS
| Exposure | Person-years | Cases | Age-adjusted HR(95% CI) | Covariate-adjusted I HR(95% CI)* | Covariate-adjusted II HR(95% CI)† |
|---|---|---|---|---|---|
| Smoking from menarche to before menopause | |||||
| 0 | 1377249 | 3871 | 1 | 1 | 1 |
| 1–10 pack-years | 568388 | 1518 | 1.01 (0.95 – 1.07) | 1.04 (0.98 – 1.11) | 1.01 (0.95 – 1.08) |
| 11–20 pack-years | 490136 | 1412 | 1.08 (1.01 – 1.14) | 1.16 (1.08 – 1.24) | 1.14 (1.06 – 1.22) |
| 21–30 pack-years | 365237 | 1123 | 1.05 (0.99 – 1.13) | 1.16 (1.08 – 1.26) | 1.15 (1.07 – 1.24) |
| ≥31 pack-years | 251164 | 891 | 1.15 (1.07 – 1.24) | 1.28 (1.18 – 1.39) | 1.27 (1.16 – 1.38) |
| P for trend | 0.0001 | <0.0001 | <0.0001 | ||
| Every 20 pack-years | 1.06 (1.03 – 1.09) | 1.11 (1.07 – 1.15) | 1.11 (1.07 – 1.15) | ||
| Smoking from menarche to before first birth | |||||
| 0 | 1493714 | 4174 | 1 | 1 | 1 |
| 1–5 pack-years | 1014089 | 2889 | 1.04 (0.99 – 1.09) | 1.12 (1.05 – 1.21) | 1.11 (1.04 – 1.20) |
| 6–10 pack-years | 340148 | 1060 | 1.14 (1.07 – 1.22) | 1.22 (1.12 – 1.33) | 1.19 (1.09 – 1.30) |
| 11–15 pack-years | 103217 | 335 | 1.18 (1.06 – 1.32) | 1.25 (1.11 – 1.41) | 1.21 (1.07 – 1.36) |
| ≥16 pack-years | 101006 | 357 | 1.22 (1.10 – 1.36) | 1.30 (1.16 – 1.46) | 1.25 (1.11 – 1.40) |
| P for trend | <0.0001 | <0.0001 | <0.0001 | ||
| Every 20 pack-years | 1.20 (1.12 – 1.28) | 1.22 (1.14 – 1.31) | 1.18 (1.10 – 1.27) | ||
| Smoking after first birth to before menopause | |||||
| 0 | 1641615 | 4678 | 1 | 1 | 1 |
| 1–10 pack-years | 580834 | 1563 | 1.02 (0.96 – 1.08) | 0.95 (0.88 – 1.04) | 0.94 (0.86 – 1.02) |
| 11–20 pack-years | 448257 | 1292 | 1.04 (0.98 – 1.11) | 0.99 (0.90 – 1.09) | 0.99 (0.90 – 1.09) |
| 21–30 pack-years | 258604 | 848 | 1.08 (1.00 – 1.16) | 1.04 (0.94 – 1.16) | 1.04 (0.94 – 1.16) |
| ≥31 pack-years | 122864 | 434 | 1.12 (1.01 – 1.23) | 1.07 (0.94 – 1.21) | 1.05 (0.92 – 1.19) |
| P for trend | 0.005 | 0.05 | 0.05 | ||
| Every 20 pack-years | 1.05 (1.01 – 1.09) | 1.04 (0.98 – 1.10) | 1.04 (0.99 – 1.10) | ||
| Smoking after menopause | |||||
| 0 | 1375058 | 4946 | 1 | 1 | 1 |
| 1–5 pack-years | 256793 | 839 | 1.00 (0.93 – 1.08) | 0.91 (0.84 – 0.99) | 0.94 (0.86 – 1.02) |
| 6–10 pack-years | 142069 | 465 | 0.94 (0.85 – 1.03) | 0.83 (0.75 – 0.92) | 0.89 (0.80 – 0.99) |
| 11–15 pack-years | 87360 | 313 | 0.96 (0.85 – 1.07) | 0.83 (0.73 – 0.94) | 0.90 (0.79 – 1.02) |
| ≥16 pack-years | 111990 | 424 | 0.94 (0.85 – 1.03) | 0.81 (0.73 – 0.91) | 0.88 (0.79 – 0.99) |
| P for trend | 0.08 | <0.0001 | 0.02 | ||
| Every 20 pack-years | 0.96 (0.89 – 1.03) | 0.87 (0.79 – 0.95) | 0.93 (0.85 – 1.02) | ||
| Smoking after menopause without hormone replacement therapy | |||||
| 0 | 965772 | 3211 | 1 | 1 | 1 |
| 1–5 pack-years | 204160 | 610 | 1.00 (0.92 – 1.10) | 0.90 (0.81 – 1.00) | 0.93 (0.84 – 1.03) |
| 6–10 pack-years | 103311 | 310 | 0.93 (0.82 – 1.04) | 0.81 (0.71 – 0.93) | 0.87 (0.76 – 0.99) |
| 11–15 pack-years | 61052 | 197 | 0.93 (0.81 – 1.08) | 0.80 (0.68 – 0.94) | 0.88 (0.75 – 1.03) |
| ≥16 pack-years | 70714 | 252 | 0.95 (0.83 – 1.08) | 0.82 (0.71 – 0.95) | 0.90 (0.78 – 1.05) |
| P for trend | 0.16 | <0.001 | 0.08 | ||
| Every 20 pack-years | 0.95 (0.86 – 1.05) | 0.86 (0.77 – 0.97) | 0.93 (0.83 – 1.05) | ||
| Smoking after menopause with hormone replacement therapy | |||||
| 0 | 401980 | 1778 | 1 | 1 | 1 |
| 1–5 pack-years | 77295 | 320 | 1.03 (0.91 – 1.16) | 1.02 (0.87 – 1.18) | 1.02 (0.87 – 1.19) |
| 6–10 pack-years | 25937 | 99 | 0.91 (0.74 – 1.12) | 0.87 (0.69 – 1.09) | 0.89 (0.70 – 1.12) |
| ≥11 pack-years | 21963 | 118 | 1.18 (0.98 – 1.43) | 1.14 (0.91 – 1.41) | 1.10 (0.88 – 1.37) |
| P for trend | 0.29 | 0.61 | 0.74 | ||
| Every 20 pack-years | 1.18 (0.97 – 1.42) | 1.15 (0.93 – 1.43) | 1.11 (0.89 – 1.39) | ||
In the assessment of smoking during specific life period, smoking during the other life periods were adjusted for.
Additionally adjusted for family history of breast cancer (yes, no), history of benign breast disease (yes, no), age at menarche (≤11, 12, 13, 14, ≥15 years), age at first birth (nulliparous, ≤24 years, 25–29 years, 30–34 years, ≥35 years), parity (0, 1, 2, 3, ≥4), OC use (never, ever for <1 year, ever for 1–4 years, ever for 5–10 years, ever for >10 years), height (continuous), current BMI (continuous), BMI at age 18 (continuous), physical activity (<1, 1–<2, 2–<4, 4–<7, ≥7 hours/week), alcohol consumption (0, 0.1–4.9, 5–14.9, ≥15 grams/day), passive smoking status at home and passive smoking status at work (never, occasional, regular). Parity and age at first birth were not adjusted for in the analysis of smoking from menarche to before first birth and analysis of smoking after first birth to before menopause. Postmenopausal hormone use (never, past for <5 years, past for ≥5 years, current for <5 years, current for ≥5 years) was adjusted in the analysis of smoking after menopause.