Table 4

 Cases of incident invasive breast cancer and related hazard ratios among 79 990 postmenopausal women by cancer subtypes and exposure to tobacco smoke

Passive smoking exposure*Active smoking status
Never†
No of cases
Any exposureNon-extensive exposure‡Extensive exposure‡Never†
No of cases
FormerCurrent
No of casesHazard ratio (95% CI)No of casesHazard ratio (95% CI)No of casesHazard ratio (95% CI)No of casesHazard ratio (95% CI)No of casesHazard ratio (95% CI)
Cases defined by histology
Ductal cancer989691.02 (0.83 to 1.26)8780.99 (0.80 to 1.23)911.20 (0.90 to 1.61)108810131.07 (0.98 to 1.18)911.16 (0.97 to 1.40)
Lobular cancer141571.22 (0.70 to 2.11)1471.25 (0.72 to 2.17)100.97 (0.43 to 2.22)1751641.08 (0.86 to 1.35)271.64 (1.09 to 2.49)
Cases defined by hormone receptor
OR+ PR+939411.04 (0.84 to 1.29)8511.01 (0.82 to 1.26)901.23 (0.91 to 1.65)105210491.12 (1.03 to 1.22)1391.28 (1.07 to 1.53)
OR+ PR–181841.14 (0.70 to 1.86)1651.09 (0.67 to 1.78)191.53 (0.79 to 2.94)2072131.18 (0.97 to 1.44)130.98 (0.63 to 1.53)
OR– PR–201601.10 (0.69 to 1.75)1931.08 (0.68 to 1.72)211.39 (0.74 to 2.58)2371941.00 (0.82 to 1.22)210.98 (0.65 to 1.49)

OR+ = oestrogen receptor positive. OR– = oestrogen receptor negative. PR+ = progesterone receptor positive. PR– = progesterone receptor negative.

*Analyses performed only among lifetime non-smokers.

†Reference categories for hazard ratios. For active smoking, all non-smokers formed the reference category regardless of passive smoking exposure.

‡Extensive exposure defined as exposure in childhood for ≥10 years, in adult home for ≥20 years, and in adult work for ≥10 years.