title: The association between lifetime smoking exposure and breast cancer mortality--results from a Norwegian cohort.
abstract: Several recent cohort studies have found an association between smoking and breast cancer, but the association between lifetime smoking exposure and breast cancer mortality is less well described. We examined whether smoking before breast cancer diagnosis is a predictor of breast cancer mortality in a large cohort with more than 4.1 million years of follow-up, with a special focus on women who initiated smoking before first childbirth. Information on smoking status was collected before breast cancer diagnosis and used to estimate hazard ratios (HRs) and corresponding 95% confidence intervals (CIs) of breast cancer mortality in a cohort of 302,865 Norwegian women with 1106 breast cancer deaths. Women were enrolled between 1974 and 2003 and followed up through linkages to national registries until 31 December 2007. We found that breast cancer mortality was slightly but significantly increased for current (HR = 1.15, 95% CI 1.01-1.32) and ever (HR = 1.15, 95% CI 1.02-1.30) smokers as compared to never smokers. No statistically significantly increased mortality was found for women who initiated smoking before first childbirth, and no dose-response association was revealed for any of the different measures of smoking exposure. A large proportion of heavy smokers may have died from other causes than breast cancer during follow-up, possibly diluting our results. This study found that lifetime smoking exposure had a significantly increased risk of breast cancer mortality compared with never smokers.
authors: Department of Community Medicine, Faculty of Health Sciences, UiT The Arctic University of Norway, N-9037, Tromsø, Norway.
authors: Eivind
authors: E
authors: Bjerkaas
authors: Ranjan
authors: R
authors: Parajuli
authors: Anders
authors: A
authors: Engeland
authors: Gertraud
authors: G
authors: Maskarinec
authors: Elisabete
authors: E
authors: Weiderpass
authors: Inger Torhild
authors: IT
authors: Gram
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology / Q000209:etiology* / Q000401:mortality*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D016016:Proportional Hazards Models; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D055815:Young Adult
keywords: Breast cancer; CONOR; cohort study; mortality; smoking