Abstract PS13-04: Impact of delayed initiation of adjuvant chemotherapy in early breast cancer: Analysis from Taiwan National breast cancer registry database
Authors: Shiau Junping , Chen Fang-Ming , Hou Ming-Feng 
Published: February 2021

Abstract
Background:In 2017, there are more than 14,000 cases of newly diagnosed breast cancer in Taiwan. With the popularity of early screening policy and social-awareness, the proportion of early breast cancer has increased significantly in the last decades. For the high risk group with early breast cancer, adjuvant systemic chemotherapy could provide lower breast cancer recurrence rate and better overall survival rate. In Taiwan, every citizen must join the National Health Insurance (NIH), and the NIH would cover the whole expanse of adjuvant chemotherapy. Theoretically, all breast cancer patients could receive their condign chemotherapy regardless of their social economic status. The optimal initiation timing of adjuvant chemotherapy is undiscovered, and the effect of delay initiation is still under contestation. In this study, we try to identify the relationship between initiation time of chemotherapy and survival outcome, and different breast cancer subtypes would be analyzed separately. We also evaluate many associated factors that may delay chemotherapy initiation or survival status.Material and Methods:In this observational, populational-based study using Taiwan national breast cancer registry database, we studied 110,784 patients diagnosed with Stage I~III breast cancer between January 1, 2006 and Deccember 31, 2016. Time to chemotherapy(TCC) was defined as the days between surgery and the initial dose of adjuvant chemotherapy. We categorized patients into initiate chemotherapy within 30 days, 31~60 days, 61~90 days, and more than 91 days. The patient demography, tumor biology, lymph node status, type of breast surgery, receiving reconstructive surgery or not, radiation therapy, immunohistochemistry data (estrogen receptor, progesterone receptor, and human epidermal growth factor 2[HER2]), and we categorized patients according to different breast cancer subtypes. Univariate analysis with Kaplan-Meier method is used to evaluate TTC influence, and log-rank test is used to compare differences between groups. Multivariate logistic regression model is used to identify important factors associated with delayed chemotherapy initiation and survival.Preliminary Results:Totally 72840 patients were enrolled in this study, and the median age at initial diagnosis was 52.4 years old. Delayed wound healing and breast reconstruction are the main factors associated with delated TTC. Comparing with TTC&lt;30 days group, TTC of 31~60 days group showed no difference in disease-free survival and overall survival, while TTC of 61~91 days group had a trend of lower disease-free survival (p=0.12). TTC more than 91 days had worse disease-free survival (HR=1.16, 95%CI=1.03~1.38) and overall survival (HR=1.23, 95%CI=1.08~1.52). We assumed initiate first chemotherapy more than 90 days as delated TTC as generally accepted in previous publications. In subgroup analysis, delayed TTC caused worse disease-free survival especially in triple negative group (HR=1.42, 95%CI=1.21~1.68) and HER2 group (HR=1.38, 95%CI=1.22~1.55).Conclusion:For breast cancer patients who assumed to receive adjuvant systemic chemotherapy, delayed in initiation of chemotherapy (more than 90 days) may result in worse outcome, especially in triple negative breast cancer and HER2 group. Besides the above preliminary result, other multivariate analysis and intergroup comparison are still ongoing. More information will reveal in SABCS 2020.
Citation Format: Junping Shiau, Fang-Ming Chen, Ming-Feng Hou. Impact of delayed initiation of adjuvant chemotherapy in early breast cancer: Analysis from Taiwan National breast cancer registry database [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS13-04.