{"doi":"10.1200/po.22.00532","title":"A Gene Panel Associated With Abemaciclib Utility in <i>ESR1</i>-Mutated Breast Cancer After Prior Cyclin-Dependent Kinase 4/6-Inhibitor Progression","abstract":"PURPOSE For patients with hormone receptor–positive (HR+), human epidermal growth factor receptor 2–negative (HER2–) metastatic breast cancer (MBC), first-line treatment is endocrine therapy (ET) plus cyclin-dependent kinase 4/6 inhibition (CDK4/6i). After disease progression, which often comes with ESR1 resistance mutations (ESR1-MUT), which therapies to use next and for which patients are open questions. An active area of exploration is treatment with further CDK4/6i, particularly abemaciclib, which has distinct pharmacokinetic and pharmacodynamic properties compared with the other approved CDK4/6 inhibitors, palbociclib and ribociclib. We investigated a gene panel to prognosticate abemaciclib susceptibility in patients with ESR1-MUT MBC after palbociclib progression. METHODS We examined a multicenter retrospective cohort of patients with ESR1-MUT MBC who received abemaciclib after disease progression on ET plus palbociclib. We generated a panel of CDK4/6i resistance genes and compared abemaciclib progression-free survival (PFS) in patients without versus with mutations in this panel (CDKi-R[–] v CDKi-R[+]). We studied how ESR1-MUT and CDKi-R mutations affect abemaciclib sensitivity of immortalized breast cancer cells and patient-derived circulating tumor cell lines in culture. RESULTS In ESR1-MUT MBC with disease progression on ET plus palbociclib, the median PFS was 7.0 months for CDKi-R(–) (n = 17) versus 3.5 months for CDKi-R(+) (n = 11), with a hazard ratio of 2.8 ( P = .03). In vitro, CDKi-R alterations but not ESR1-MUT induced abemaciclib resistance in immortalized breast cancer cells and were associated with resistance in circulating tumor cells. CONCLUSION For ESR1-MUT MBC with resistance to ET and palbociclib, PFS on abemaciclib is longer for patients with CDKi-R(–) than CDKi-R(+). Although a small and retrospective data set, this is the first demonstration of a genomic panel associated with abemaciclib sensitivity in the postpalbociclib setting. Future directions include testing and improving this panel in additional data sets, to guide therapy selection for patients with HR+/HER2– MBC.","journal":"JCO Precision Oncology","year":2023,"id":339667,"datarank":0.42498200160843247,"base_score":2.833213344056216,"endowment":2.833213344056216,"self_citation_contribution":0.42498200160843247,"citation_network_contribution":0.0,"self_endowment_contribution":0.42498200160843247,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":16,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9613,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2023-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":243917,"name":"Taronish D. 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