Table 2.
Smoking status and pack-years of smoking in relation to the incidence of breast cancer among 111,140 participants in the NHS with follow-up from 1976 to 2006.
| Smoking status | Person-years | Cases | Age-adjusted HR(95% CI) | Covariate-adjusted I HR(95% CI)* | Covariate-adjusted II HR(95% CI)† |
|---|---|---|---|---|---|
| Smoking Status | |||||
| Never | 1341442 | 3788 | 1.0 | 1.0 | 1.0 |
| Ever: | 1664421 | 4984 | 1.07 (1.03 – 1.12) | 1.06 (1.01 – 1.10) | 1.07 (1.02 – 1.12) |
| Current | 586952 | 1422 | 1.02 (0.96 – 1.09) | 1.05 (0.98 – 1.12) | 1.09 (1.02 – 1.17) |
| Past | 1077469 | 3562 | 1.09 (1.04 – 1.14) | 1.06 (1.01 – 1.11) | 1.06 (1.01 – 1.11) |
| Total smoking after menarche | |||||
| 0 | 1341442 | 3788 | 1.0 | 1.0 | 1.0 |
| 1–10 pack-years | 528586 | 1419 | 1.03 (0.97 – 1.09) | 1.00 (0.94 – 1.07) | 1.00 (0.94 – 1.07) |
| 11–20 pack-years | 418217 | 1155 | 1.08 (1.02 – 1.16) | 1.07 (1.00 – 1.14) | 1.08 (1.01 – 1.16) |
| 21–30 pack-years | 330255 | 949 | 1.03 (0.96 – 1.10) | 1.04 (0.97 – 1.12) | 1.07 (1.00 – 1.15) |
| 31–40 pack-years | 205490 | 713 | 1.10 (1.02 – 1.19) | 1.12 (1.03 – 1.21) | 1.16 (1.07 – 1.26) |
| 41–50 pack-years | 108847 | 365 | 0.98 (0.88 – 1.09) | 1.01 (0.90 – 1.12) | 1.05 (0.94 – 1.18) |
| ≥51 pack-years | 90966 | 365 | 1.11 (1.00 – 1.24) | 1.14 (1.02 – 1.28) | 1.19 (1.07 – 1.33) |
| P for trend | 0.04 | 0.005 | <0.0001 | ||
| Ever 20 pack-years | 1.03 (1.01 – 1.06) | 1.04 (1.01 – 1.07) | 1.06 (1.03 – 1.09) | ||
Covariate-adjusted I was adjusted for age (continuous), family history of breast cancer (yes, no), age at menarche (≤11, 12, 13, 14, ≥15 years), height (continuous), BMI at age 18 (continuous), OC use (never, ever for <1 year, ever for 1–4 years, ever for 5–10 years, ever for >10 years), history of benign breast disease (yes, no), leisure time 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 at home and at work (never, occasional, regular), age at first birth (nulliparous, ≤24 years, 25–29 years, 30–34 years, ≥35 years), parity (0, 1, 2, 3, ≥4), and current BMI (continuous).
Covariate-adjusted II was additionally adjusted for age at menopause (continuous), menopausal status (premenopause, postmenopause, dubious), and postmenopausal hormone use (never, past for <5 years, past for ≥5 years, current for <5 years, current for ≥5 years).