ESTRO 2025 - Abstract Book

S640

Clinical - Breast

ESTRO 2025

vs 3.0 [2.3-3.4]). Within the adjuvant RT cohort, 7 (39%) of the 18 patients with reported pCR at surgery had detectable CTCs immediately prior to RT, while 3 (16%) remained CTC-Positive at the end of RT. All 3 patients achieved CTC clearance at the “Post-RT” timepoint (3.4 months [2.9,4.5] after RT).

Conclusion: In this prospective analysis, advanced nodal disease and IBC were associated with detection of CTCs prior to adjuvant RT; 39% of patients with pCR were CTC-positive. Following comprehensive RT, 100% of CTC-positive patients experienced clearance. While delayed CTC clearance without RT cannot be assessed on this single arm study, these results support further study of longitudinal monitoring of circulating tumor material as a potential real-time biomarker for residual locoregional disease prior to RT as well as a potential surrogate for radiotherapeutic efficacy.

Keywords: CTCs, circulating tumor material, biomarker

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