Abstract P3-08-36: The effects of smoking and smoking cessation on postmenopausal breast cancer recurrence -Results from the Cohort 05 of the Rainbow of KIBOU (ROK) study: A prospective breast cancer survivor cohort in Japan
Authors: Yuri Mizota, Takuji Iwase, Yasuo Ohashi, Hirofumi Mukai, Seiichiro Yamamoto
Journal: Cancer Research (2020)

Abstract [Background] Smoking is an established risk factor for breast cancer incidence. As for breast cancer prognosis, the effect of patient’s smoking on her mortality is also substantial. However, there are very few reports of investigating patient’s smoking and smoking cessation effects on breast cancer recurrence, especially those with controlling for treatment effects. [Methods] We conducted a prospective cohort study (Cohort 05 of the Rainbow of KIBOU study) for the patients enrolled in the N-SAS BC 05 trial (AERAS, UMIN:000000818). The N-SAS BC 05 trial is the randomized multi-center open-label phase III trial to assess the effect of the extended use of anastrozole for an additional 5 years where postmenopausal patients with stage I-III, hormone-receptor-positive breast cancer, disease-free after 5 years of either anastrozole alone or tamoxifen 2-3 years followed by anastrozole 3-2 years were randomized to continual group with anastrozole for an additional 5 years or stop group without an additional anastrozole. Our primary end point was disease-free survival. Since the data came from well controlled randomized trial of treatment comparison, precise recurrence and treatment data were available. [Results] We enrolled 1,510 women from the participants of the NSAS BC 05 trial. After a median follow up of 5.1 years, there were 144 events including breast cancer recurrences, secondary cancers, and deaths. The 5-year disease-free survival rates from the entry of the study (10 year from diagnosis) were 89.4% (95% confidence interval [CI], 87.4 to 91.5) in nonsmokers, 87.7% (95% CI: 82.0 to 93.4) in quitters (both before and after diagnosis), and 76.1% (95% CI, 62.7 to 89.4) in smokers (P=0.02 by a two sided log-rank test). Hazard ratios are 2.13 (95% CI, 1.14 to 3.97) for smokers and 1.35 (95% CI, 0.83 to 2.20) for quitters compared to nonsmokers after controlling treatment and age effects. If the quitters were divided into two groups by the time of cessation, hazard ratios are 1.31 (95% CI, 0.74 to 2.34) for those who quitted before diagnosis and 1.47 (95% CI, 0.64 to 3.34) for those who quitted after diagnosis. The results were not substantially changed if the events were restricted to recurrence. [Conclusion] Ten year disease-free survival for smokers was significantly worse than that of nonsmokers after almost perfectly controlling treatment effects. Compared to that, 10 year disease-free survival for quitters was not different from that of nonsmokers. The risk was decreased if they quit smoking even after diagnosis. Our study shows the importance of smoking cessation for breast cancer patients. Citation Format: Yuri Mizota, Takuji Iwase, Yasuo Ohashi, Hirofumi Mukai, Seiichiro Yamamoto. The effects of smoking and smoking cessation on postmenopausal breast cancer recurrence -Results from the Cohort 05 of the Rainbow of KIBOU (ROK) study: A prospective breast cancer survivor cohort in Japan [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-08-36.