Blood-based monitoring identifies acquired and targetable driver HER2 mutations in endocrine-resistant metastatic breast cancer

Abstract

Plasma genotyping identifies potentially actionable mutations at variable mutant allele frequencies, often admixed with multiple subclonal variants, highlighting the need for their clinical and functional validation. We prospectively monitored plasma genotypes in 143 women with endocrine-resistant metastatic breast cancer (MBC), identifying multiple novel mutations including HER2 mutations (8.4%), albeit at different frequencies highlighting clinical heterogeneity. To evaluate functional significance, we established ex vivo culture from circulating tumor cells (CTCs) from a patient with HER2 -mutant MBC, which revealed resistance to multiple targeted therapies including endocrine and CDK 4/6 inhibitors, but high sensitivity to neratinib (IC50: 0.018 μM). Immunoblotting analysis of the HER2 -mutant CTC culture line revealed high levels of HER2 expression at baseline were suppressed by neratinib, which also abrogated downstream signaling, highlighting oncogenic dependency with HER2 mutation. Furthermore, treatment of an index patient with HER2 -mutant MBC with the irreversible HER2 inhibitor neratinib resulted in significant clinical response, with complete molecular resolution of two distinct clonal HER2 mutations, with persistence of other passenger subclones, confirming HER2 alteration as a driver mutation. Thus, driver HER2 mutant alleles that emerge during blood-based monitoring of endocrine-resistant MBC confer novel therapeutic vulnerability, and ex vivo expansion of viable CTCs from the blood circulation may broadly complement plasma-based mutational analysis in MBC.

Targeting Cell Cycle in Breast Cancer: CDK4/6 Inhibitors

“…NRAS, FGFR2, and ERBB2 have been associated to CDK4/6i resistance and/or antiestrogen resistance in whole exome analysis of tumor specimens [132]. Also point mutations in ERBB2 have been associated with palbociclib and antiestrogen resistance; this resistance can, in vitro, be reverted by adding the HER2 kinase inhibitor neratinib [133,134]. The prospective, pharmacogenetic study ECLIPS is identifying predictive biomarkers in response to palbociclib plus ET combination treatment; results showed that the thymidine kinase-1 (TK1), key regulator of S/G2 phase, was significantly increased before treatment when compared after 3 months of treatment in patients who experienced disease progression, suggesting that TIK1 mRNA copies/mL can be correlated to acquired resistance to CDK4/6i [135].…”

The Lipogenic Regulator SREBP2 Induces Transferrin in Circulating Melanoma Cells and Suppresses Ferroptosis

“…We have previously reported the establishment of long-term CTC cultures from blood specimens of women with hormone-receptor positive breast cancer, which are often oligoclonal in origin, and which recapitulate somatic mutations acquired during the course of therapy, and their epigenetic cell states (25)(26)(27). Here, we established CTC cultures from blood samples of patients with metastatic melanoma, comparing their transcriptomes across different cases, as well as in multiple single CTC-derived isogenic lines from the same patient.…”

Methodological Advancements for Investigating Intra-tumoral Heterogeneity in Breast Cancer at the Bench and Bedside

“…A study of ER+/PR+/HER2 − metastatic breast cancer patients demonstrated the emergence of acquired HER2 mutations in circulating tumor cells (CTCs) isolated from 143 patients who had developed endocrine therapy resistance. Treatment with neratinib, an irreversible HER2 inhibitor, resulted in significant clinical responses, supporting the use of CTC analyses to monitor molecular heterogeneity that emerges as tumors resist therapy [ 124 ].…”