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.

Differences in breast cancer-risk factors between screen-detected and non-screen-detected cases (MCC-Spain study)

“…Our results do not conclusively confirm associations with other known lifestyle-related risk factors [3,4], such as tobacco use [39][40][41][42][43] and alcohol consumption [6,[44][45][46][47]; this could be due to the limitations of the study, which are outlined later in this section.…”

The fraction of breast cancer attributable to smoking: The Norwegian women and cancer study 1991–2012

“…However, results from several recent cohort studies, not included in the above-listed expert reports, on smoking and breast cancer incidence ( Bjerkaas et al , 2013 ; Gaudet et al , 2013 ; Rosenberg et al , 2013 ; Dossus et al , 2014 ; Nyante et al , 2014 ; Catsburg et al , 2015 ; Gram et al , 2015 ) and mortality ( Bjerkaas et al , 2014 ; Carter et al , 2015 ) suggest that the burden of smoking on society is underestimated.…”

Hormonal contraception increases risk of breast tumor based on clinical breast examination among adult women

“…While 10% of females who continued to smoke after diagnosis, had a 1.7-fold higher risk of dying from breast cancer (HR=1.72; 95% CI: 1.13-2.60), as compared with nonsmoking. According to Bjerkaas et al, (43) several large prospective cohort studies have found that smoking can cause breast cancer, especially in females who smoke for an extended period of time, those who smoke a great number of cigarettes per day and those who smoke before delivering their first child. Their research results showed that the mortality from breast cancer may indeed be low, but increases significantly for active smoking (current) and former smoking (HR=1.15; 95% CI: 1.01-1.32 and HR=1.15; 95% CI: 1.02-1.30, respectively), as compared with nonsmoking.…”