Background
tumor
TUMOR
The combination of a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) and endocrine therapy (ET) has become the new standard of care for patients with hormone receptor–positive, human epidermal growth factor receptor-2–negative (HR + /HER2 −) advanced breast cancer (ABC) [MONALEESASIA included dose-escalation and dose-expansion phases of ribociclib plus ET (letrozole, fulvestrant, or tamoxifen plus goserelin) in patients with HR + /HER2 − ABC in Japan, Hong Kong, and Singapore [Although tumor biopsy remains the preferred clinical diagnostic method in oncology, liquid biopsy technologies have been increasingly adopted to obtain predictive and prognostic data [However, limited data are available on longitudinal ctDNA analysis of gene alterations following treatment with CDK4/6i for ABC. Most reports have focused on early ctDNA changes in order to correlate ctDNA with response to treatment [