Fig. 1: Description of the study.

a Blood samples were extracted at baseline and after 1 cycle (i.e. 4 weeks) in patients with metastatic HR+/HER2-negative BC treated with CDK4/6i plus ET. b The list of 74 genes analyzed by Guardant360. c CONSORT diagram. d Frequency of gene mutations with ≥VAF 0.4% at baseline identified in the patient dataset and Venn diagram with the 4 most frequent mutations. e PAM50 distribution (LumA = Luminal A, LumB=Luminal B, HER2E = HER2-enriched). *PD Progressive disease, pts patients, M1 metastatic.