Although a recent study in 33 patients receiving palliative CDK4/6i reported that serial ctDNA monitoring with a 52-gene assay predicted disease progression with a 2- to 3-month lead time, [17] few studies in ABC have tracked and reported ctDNA dynamics with large gene panels and concurrent measurements using Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1). Here, CDK4 is linked to aneurysmal bone cyst.