Conclusion
PD
TUMOR PROGRESSION
Ribociclib plus ET decreased ctDNA levels in Asian patients who responded to treatment with HR + /HER2 − ABC, regardless of starting dose. ctDNA levels at baseline correlated with PFS, and ctDNA increases during treatment allowed the identification of PD in a significant fraction of patients before it was detected by radiological methods. While this analysis is hypothesis generating, the results demonstrate the potential of measuring ctDNA throughout treatment to detect tumor progression, as well as of identifying genetic alterations that have clinical implications in HR + /HER2 − ABC.