Impacts of smoking on endocrine treatment response in a prospective breast cancer cohort

Background: The association between smoking and breast cancer prognosis remains unclear. The purpose of this study was to investigate whether preoperative smoking was associated with prognosis in different treatment groups. Methods: This population-based cohort consisted of 1065 breast cancer patients without preoperative treatment included between 2002 and 2012 in Lund, Sweden. Smoking status was examined in relation to patient and tumour characteristics, and prognosis in different treatment groups. Results: At the preoperative visit, 21.0% smoked. Median follow-up time was 5.1 years. Overall, in the 1016 patients included in the survival analyses, there was no significant association between smoking and risk of breast cancer events (adjusted hazard ratio (adjHR): 1.45; 95% confidence interval (CI): 0.95-2.20). For the 309 aromatase inhibitor (AI)-treated patients >= 50 years with oestrogen receptor-positive (ER+) tumours, smoking was associated with risk of breast cancer events (adjHR: 2.97; 95% CI: 1.44-6.13), distant metastasis (adjHR: 4.19; 95% CI: 1.81-9.72), and death (adjHR: 3.52; 95% CI: 1.59-7.81). Smoking was not associated with breast cancer events or distant metastasis in other treatment groups. Conclusions: Preoperative smoking was only associated with an increased risk for breast cancer events and distant metastasis in AI-treated patients. If confirmed, smoking status should be taken into consideration when selecting an endocrine therapy.