Passive smoking and risk of breast cancer in the California teachers study.
BACKGROUND
Although recent reviews have suggested active smoking to be a risk factor for breast cancer, the association with passive smoke exposure remains controversial. This risk association was explored in a large prospective study of women, the California Teachers Study.


METHODS
Detailed lifetime information on passive smoke exposure by setting (home, work, or social) and by age of exposure was collected in 1997 from 57,523 women who were lifetime nonsmokers and had no history of breast cancer. In the ensuing decade, a total of 1,754 women were diagnosed with invasive breast cancer. Cox proportional hazards models were fit to estimate hazard ratios (HR) and 95% confidence intervals (95% CI) associated with several lifetime passive smoke exposure metrics.


RESULTS
For all breast cancer, measures of higher lifetime passive smoking intensity and duration were associated with nonstatistically significant HRs of 1.11 to 1.14. For postmenopausal women, HRs for lifetime low, medium, and high cumulative exposure were 1.17 (95% CI, 0.91-1.49), 1.19 (95% CI, 0.93-1.53), and 1.26 (95% CI, 0.99-1.60). For women exposed in adulthood (age > or =20 years), risk was elevated at the highest level of cumulative exposure (HR, 1.18; 95% CI, 1.00-1.40), primarily among postmenopausal women (HR, 1.25; 95% CI, 1.01-1.56). A statistically significant dose response was detected when analysis was restricted to women with moderate to high levels of passive smoke exposure.


CONCLUSIONS
These results suggest that cumulative exposures to high levels of sidestream smoke may increase breast cancer risk among postmenopausal women who themselves have never smoked tobacco products.
Reynolds
Peggy
P
Northern California Cancer Center, Berkeley, 94704, USA. preynolds@nccc.org
Goldberg
Debbie
D
Hurley
Susan
S
Nelson
David O
DO
Largent
Joan
J
Henderson
Katherine D
KD
Bernstein
Leslie
L
D000328:Adult; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology*; D002140:California / Q000453:epidemiology; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D011379:Prognosis; D011446:Prospective Studies; D012307:Risk Factors; D015996:Survival Rate; D013663:Teaching; D014028:Tobacco Smoke Pollution / Q000009:adverse effects*; D055815:Young Adult
D014028:Tobacco Smoke Pollution