1. In a prospective cohort study of over 4500 women with invasive breast cancer, patients with smoking exposure were associated with increased mortality compared to patients with no exposure to smoking.
2. Breast cancer patients who quit smoking demonstrated lower mortality from respiratory cancers and cardiovascular diseases compared to those who continued to smoke.
Evidence Rating Level: 2 (Good)
Study Rundown: In addition to its association with cardiovascular disease, cigarette smoking has been found to be a prognostic factor for breast cancer-specific mortality. However, there has been limited analysis of the long-term effects of smoking among breast cancer survivors, particularly those who continue to smoke after their diagnosis. The purpose of this prospective cohort study was to evaluate the association with smoking both before and after breast cancer diagnosis and long-term mortality.
The study prospectively followed health outcomes data and self-reported smoking status for over 20 000 breast cancer survivors between 1988 and 2008. At the conclusion of the study, women who actively smoked prior to breast cancer diagnosis demonstrated a 25% increase in overall mortality compared to never smokers. Patients who continued to smoke post-breast cancer diagnosis demonstrated a significant increase in both cancer-specific and overall mortality. Patients who quit smoking after breast cancer diagnosis demonstrated a 9% risk reduction in overall mortality. This was the largest study to date to analyze the effect of smoking on breast cancer survival. The study was limited by the use of self-reported smoking status which may lead to recall bias as well as a lack of information on the association of smoking on specific breast cancer hormone receptor subtypes. However, these findings demonstrate the importance of promoting smoking cessation in breast cancer survivors.
In-Depth [prospective cohort]: The authors analyzed breast cancer survival data from two large prospective cohort databases from the United States: the Collaborative Breast Cancer Study (CBCS) and the Collaborative Women’s Longevity Study (CWLS). Smoking status was ascertained via self-reported survey for patients in both databases. Smoking status was defined as follows: never smoker and active smoker (within 1 year of survey). Patients were excluded from this study if they had missing smoking data, unknown cancer staging, distant disease, or recurrent disease. The primary outcomes were survival times from time of diagnosis. Overall, 20 691 and 4562 women were reviewed from the CBCS and CWLS, respectively. After a median follow-up of 12 years, active smokers demonstrates significantly higher cancer-specific mortality (HR: 1.25; 95% CI: 1.13 to 1.37) and increased incidence of respiratory cancers (HR: 14.48; 95% CI: 9.89 to 21.21) and cardiovascular disease (HR: 2.08; 95% CI: 1.80 to 2.41) compared to never smokers. Patients who continued to smoke beyond their breast cancer diagnosis demonstrated significantly increased risk of cancer-specific mortality (HR: 1.72; 95% CI: 1.13 to 2.60) compared to never smokers. Quitting smoking after cancer diagnosis significantly reduced mortality from respiratory cancer (HR: 0.39; 95% CI: 0.16 to 0.95). Additionally, quitting smoking also demonstrated a trend towards lower mortality from breast cancer (HR: 0.67; 95% CI: 0.38 to 1.19).
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