Active and passive smoking in breast cancer: prospective results from the Nurses' Health Study.
BACKGROUND
The role of active and passive smoking in breast cancer remains controversial.


METHODS
Using data collected in the prospective Nurses' Health Study, we examined the influence of active and passive smoking on the incidence of invasive breast cancer. The analysis was based on women responding to the 1982 questionnaire, which included questions on passive smoking exposure. Information on active smoking was collected in biennial questionnaires. A total of 78,206 women were followed prospectively from 1982 until June 1996.


RESULTS
Of these women, 3,140 reported a diagnosis of invasive breast cancer during follow-up. Compared with never active smoking, relative risks (RR) of breast cancer were 1.04 (95% CI = 0.94-1.15) for current active smoking and 1.09 (95% CI = 1.00-1.18) for past active smoking. The RR for regular passive exposure at work and at home was 0.90 (95% CI = 0.67-1.22). For active smoking, a modest increase in risk was confined to women who began smoking before the age of 17 (RR = 1.19; 95% CI = 1.03-1.37).


CONCLUSIONS
Results suggest that passive smoking is unrelated to breast cancer. However, results for active smoking are compatible with a small increase in risk when smoking is initiated at young ages.
Egan
Kathleen M
KM
Department of Epidemiology, Harvard School of Public Health, Boston, MA 02115, USA. kegan@hsph.harvard.edu
Stampfer
Meir J
MJ
Hunter
David
D
Hankinson
Susan
S
Rosner
Bernard A
BA
Holmes
Michelle
M
Willett
Walter C
WC
Colditz
Graham A
GA
D000328:Adult; D001943:Breast Neoplasms / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015999:Multivariate Analysis; D009726:Nurses; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D014028:Tobacco Smoke Pollution / Q000009:adverse effects*
D014028:Tobacco Smoke Pollution