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Ref Type Journal Article
PMID (29236940)
Authors Condorelli R, Spring L, O'Shaughnessy J, Lacroix L, Bailleux C, Scott V, Dubois J, Nagy RJ, Lanman RB, Iafrate AJ, Andre F, Bardia A
Title Polyclonal RB1 mutations and acquired resistance to CDK 4/6 inhibitors in patients with metastatic breast cancer.
Journal Annals of oncology : official journal of the European Society for Medical Oncology
Vol 29
Issue 3
Date 2018 Mar 01
URL
Abstract Text While deregulation of the cyclin D1-CDK4/6-retinoblastoma pathway is common in hormone receptor positive (HR+) breast cancer, Rb is usually intact in HR+ breast cancer, and targeted CDK 4/6 inhibitors that act upstream of Rb, are routinely being utilized in clinical practice. However, factors that can lead to clinical resistance to CDK 4/6 inhibitors are not known.We identified patients who had pre- and post-genotyping in tissue and peripheral blood samples after receiving CDK 4/6 inhibitors. Genotyping was carried out in tumor tissue or blood collected before start of CDK 4/6 inhibitor and after disease progression on CDK 4/6 inhibitor, covering more than 90% of the coding region in RB1.We identified detectable acquired RB1 mutations in circulating tumor DNA (ctDNA) after exposure to CDK4/6 inhibitor (palbociclib, palbociclib, ribociclib) for 5, 8, and 13 months, respectively, in three patients. The RB1 mutations included substitution in donor splicing site of exon 8 of the RB1 gene in patient #1; substitution in donor splicing site of exon 22 of RB1 gene, exon 19 deletion, exon 3 insertion in patient #2; and RB1 exon 16 H483Y mutation in patient #3. None of these RB1 mutations were present in the pre-CDK 4/6 specimen highlighting these molecular alterations, which lead to functional loss of Rb1, likely emerged under selective pressure from the CDK4/6 inhibitor potentially confering therapeutic resistance.This is the first clinical report to describe the emergence of somatic RB1 mutations after exposure to palbociclib or ribociclib, in patients with metastatic breast cancer. Further research is needed to validate these findings, identify how these mutations temporally emerge under selective pressure of CDK 4/6 inhibitor, and develop rational therapeutic strategies.

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Molecular Profile Treatment Approach
Gene Name Source Synonyms Protein Domains Gene Description Gene Role
Therapy Name Drugs Efficacy Evidence Clinical Trials
Drug Name Trade Name Synonyms Drug Classes Drug Description
Gene Variant Impact Protein Effect Variant Description Associated with drug Resistance
RB1 H483Y missense unknown RB1 H483Y lies within domain A of the Rb1 protein (UniProt.org). H483Y has been identified in the scientific literature (PMID: 29236940), but has not been biochemically characterized and therefore, its effect on Rb1 protein function is unknown (PubMed, Mar 2020).
RB1 T738_R775del deletion unknown RB1 T738_R775del results in the deletion of 38 amino acids in domain B of the Rb1 protein from amino acids 738 to 775 (UniProt.org). T738_R775del has been identified in the scientific literature (PMID: 29236940), but has not been biochemically characterized and therefore, its effect on Rb1 protein function is unknown (PubMed, Mar 2020).
Molecular Profile Indication/Tumor Type Response Type Therapy Name Approval Status Evidence Type Efficacy Evidence References
RB1 H483Y Her2-receptor negative breast cancer predicted - resistant Letrozole + Ribociclib Case Reports/Case Series Actionable In a clinical case study, RB1 H48Y was identified in the circulating tumor DNA of a patient with estrogen receptor positive, progesterone receptor positive, and Erbb2 (Her2)-negative, invasive ductal carcinoma at the time of disease progression after 13 months of Kisqali (ribociclib) and Femara (letrozole) combination treatment (PMID: 29236940). 29236940
RB1 I101fs RB1 E268* RB1 V654fs RB1 T738_R775del Her2-receptor negative breast cancer predicted - resistant Fulvestrant + Palbociclib Case Reports/Case Series Actionable In a clinical case study, RB1 mutations including E268*, I101fs, T738_R775del, and V654fs were identified in the circulating tumor DNA of a patient with estrogen receptor positive, progesterone receptor positive, and Erbb2 (Her2)-negative, invasive ductal carcinoma at the time of disease progression after 8 months of Ibrance (palbociclib) and Faslodex (fulvestrant) combination treatment (PMID: 29236940). 29236940