CDK4 and breast cancer: In another study, the genomic analysis of 24 tumor and 17 ctDNA samples obtained from patients treated with exemestane plus everolimus and palbociclib, triplet therapy for CDK4/6i-resistant BC, found ERBB2 amplification in several tumors and identified a patient with coexisting tumor lineages with distinct activating ERBB2 mutations, suggesting that HER2 activation may follow CDK4/6i therapy [150].