Abstract PD5-07: Prospective Analysis of Circulating Tumor Cell Clearance and Dynamics with Adjuvant Radiotherapy in Locally Advanced Breast Cancer

Abstract Background: Detection of circulating tumor cells (CTCs) is a strong prognostic biomarker for clinical outcomes in non-metastatic breast cancer. The kinetics of CTC clearance with adjuvant radiotherapy (RT) and its utility as a predictive biomarker have not been well characterized. Here we present the results of a prospective observational cohort study evaluating the dynamics of CTC detection and response to adjuvant breast radiotherapy. Methods: Patients with clinical or pathologic T3-4 or node-positive non-metastatic breast cancer dispositioned to receive comprehensive regional nodal irradiation (RNI) were prospectively enrolled. CTCs were enumerated using the CellSearch® assay immediately prior to RT (Pre-RT), within 1 week of RT (End of RT), and at follow-up 3-6 months following RT (Post-RT). Rates of CTC detection at each time point and clearance with RT were estimated. Associations between CTC status with clinicopathologic and treatment variables were performed using McNemar’s Exact, Wilcoxon, Fisher’s Exact, or Mann Whitney U Tests, as appropriate. For all applicable analyses, statistical significance was defined as a P-value of