Table 2.

 Cases of incident invasive breast cancer and related hazard ratios associated with exposure to passive smoking among 41 022 postmenopausal women who had never smoked

Exposure to passive smoking	No of cases	Hazard ratio (95% Cl)
		Age adjusted	Multivariable adjusted*
None	145	1.00 (reference)	1.00 (reference)
Any:	1515	1.08 (0.91 to 1.28)	1.09 (0.92 to 1.29)
Childhood only	110	1.22 (0.95 to 1.56)	1.19 (0.93 to 1.53)
Adult at home only	88	0.89 (0.69 to 1.16)	0.91 (0.70 to 1.19)
Adult at work only	199	1.02 (0.83 to 1.27)	1.01 (0.82 to 1.26)
Childhood + adult at home	170	1.02 (0.81 to 1.27)	1.04 (0.83 to 1.30)
Childhood + adult at work	191	1.18 (0.95 to 1.47)	1.17 (0.94 to 1.45)
Adult at home + at work	236	1.12 (0.91 to 1.38)	1.15 (0.93 to 1.41)
Childhood + adult at home + at work	521	1.09 (0.90 to 1.31)	1.11 (0.92 to 1.34)
Cumulative exposure categories:
No childhood + any adult	524	1.04 (0.86 to 1.24)	1.05 (0.87 to 1.26)
Childhood <10 years + any adult	154	1.10 (0.88 to 1.39)	1.13 (0.90 to 1.42)
Childhood ≥10 years + adult at home <20 years + adult at work <10 years	421	1.14 (0.95 to 1.38)	1.13 (0.94 to 1.37)
Childhood ≥10 years + adult at home <20 years + adult at work ≥10 years	151	0.99 (0.79 to 1.24)	0.98 (0.77 to 1.23)
Childhood ≥10 years + adult at home ≥20 years + adult at work <10 years	124	0.99 (0.78 to 1.25)	1.05 (0.82 to 1.33)
Childhood ≥10 years + adult at home ≥20 years + adult at work ≥10 years†	146	1.27 (1.01 to 1.60)	1.32 (1.04 to 1.67)
P value for trend§		0.16	0.10

*Variables used in multivariable models included age at enrolment, ethnicity, education, body mass index, physical activity, alcohol intake, parity, family history of breast cancer, hormone therapy use, age at menarche, and age of first live birth.

†The “extensive exposure” variable defined a priori.

§Including the reference group (no exposure) and the 6 rows of cumulative exposure categories.