Abstract P5-08-29: Tamoxifen or aromatase inhibitors: Should smoking status impact on selection of endocrine therapy in breast cancer patients?
Authors: Jernström H , Persson M , Simonsson M , Markkula A , Rose C , Ingvar C 
Published: May 2016

Introduction: The association between smoking and breast cancer prognosis has been investigated in several studies but remains unclear. To our knowledge, no study has investigated whether the response to different endocrine treatments differs between smokers and non-smokers. Smoking can suppress aromatase activity, but also increase inflammation, which may lead to higher activity. The aim was to investigate whether preoperative smoking was associated with risk of breast cancer events in endocrine-treated patients.

Patients and methods: This population based cohort consisted of 1026 female breast cancer patients with invasive tumors and no preoperative treatment who were enrolled in an ongoing prospective cohort study at Skåne University Hospital in Lund between October 2002 and June 2012. Pre- and postoperative questionnaires regarding lifestyle factors, including smoking status, and treatments were completed. Information on tumor characteristics, treatments, and dates for new breast cancer events or deaths was obtained from pathology reports, patients' charts and population registers. A breast cancer event was defined as local or regional recurrence, contralateral breast cancer, or distant metastasis.

Results: For the survival analyses, two patients were excluded due to missing information on smoking and eight patients were excluded due to metastatic spread within 0.3 years of inclusion, leaving 1016 patients of which 206 (20.3%) reported preoperative smoking. Less than 1% of the 810 preoperative non-smokers reported smoking at either the 3-6-months or 1-year postoperative visits, while about 10% of the patients who smoked preoperatively reported not to smoke during the follow-up visits. Thus, the majority of the patients did not switch smoking status. Patients were followed for up to 11 years (median 5.1 years for patients still at risk). Overall, there was no significant association between smoking and risk of breast cancer events (adjusted hazard ratio (HR) 1.45: 95% CI 0.95-2.20; P=0.08) adjusted for patient and tumor characteristics. For the 408 tamoxifen-treated patients aged 50 years or older with estrogen receptor positive tumors, smoking was not significantly associated with risk for early events (adjusted HR 1.58: 95% CI 0.76-3.30; P=0.22). However, for the 309 aromatase inhibitor-treated patients aged 50 years or older with estrogen receptor positive tumors, smoking was significantly associated with a 3-fold increased risk of breast cancer events (adjusted HR 2.97: 95% CI 1.44-6.12; P=0.003). Some patients had been treated with sequential tamoxifen and aromatase inhibitor therapy.

Conclusions: Preoperative smoking was associated with a significantly increased risk for breast cancer events among patients treated with aromatase inhibitors, but not among tamoxifen-treated patients. If confirmed, smoking status should be taken into consideration when selecting endocrine therapy.

Citation Format: Jernström H, Persson M, Simonsson M, Markkula A, Rose C, Ingvar C. Tamoxifen or aromatase inhibitors: Should smoking status impact on selection of endocrine therapy in breast cancer patients?. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-08-29.