In the present study, we did not observe any association between TKa and tumor Ki67 or SBR grade, which could be explained by the time-lag between determination of Ki67 or SBR grade, assessed on the primary tumor, and determination of pTKa in an advanced metastatic setting (as no tumor biopsy of metastasis was available at the start of ET+ CDK4/6 treatment). Here, CDK4 is linked to neoplasm.