Short report: Monitoring ESR1 mutations by circulating tumor DNA in aromatase inhibitor resistant metastatic breast cancer

Abstract

Acquired estrogen receptor gene (ESR1) mutations have been recently reported as a marker of resistance to aromatase inhibitors in hormone receptor positive metastatic breast cancer. We retrospectively considered seven patients treated for metastatic breast cancer with available samples from the primary tumor before any treatment, cryopreserved metastasis removed during progression and concomitant plasmas. All these seven patients were in disease progression after previous exposure to aromatase inhibitors for at least 6 months, and were assessed for ESR1 mutations detection in tumor and circulating DNA. For these patients, Sanger sequencing identified four metastases with clear ESR1 mutation and one possible, whereas digital PCR identified six mutated metastases. Then, under blind conditions and using digital PCR, corresponding circulating ESR1 mutations were successfully detected in four of these six metastatic breast cancer patients. Moreover, in two patients with serial blood samples following treatments exposure, the monitoring of circulating ESR1 mutations clearly predicted disease evolution. In the context of high interest for ESR1 mutations, our results highlight that these acquired recurrent mutations may be tracked in circulating tumor DNA and may be of clinical relevance for metastatic breast cancer patient monitoring.Nearly 70% of breast cancers are hormone receptor positive (HR1) and potentially sensitive to hormonal therapy. Aromatase inhibitors (AI) or tamoxifen is the recommended first line hormonal therapy in postmenopausal HR1 metastatic breast cancer (MBC).1,2 Nevertheless, disease progression is usually observed within a few months after treatment initiation.3,4 Acquired resistance to hormonal therapy may be based on activating mutations in the estrogen receptor gene (ESR1). These mutations have been detected in HR1 MBC patients previously exposed to hormonal therapy, including treatment with an AI in all cases. The frequencies of ESR1 mutations was 25% (nine of 36), 38% (five of 13) and 54% (six of 11) among these cohorts. [5][6][7] Approximately 12 ESR1 point mutations have been described, with a hot spot confined to codons 537 and 538 in exon 8. 8 These mutations result in a ligand-independent estrogen receptor (ER) activity. In vitro and preclinical data suggest that ESR1 mutations lead to complete AI resistance and to partial resistance to ER agonists and antagonists.9,10 The detection of ESR1-activating mutations may be relevant for guiding clinicians between endocrine and nonendocrine therapy.11 Thus far, ESR1 genotyping must be performed on metastases: this method is hardly compatible with repetitive sampling analyses for disease monitoring. Circulating tumor DNA (ctDNA) analysis is considered a promising tool for providing relevant prognostic and/or predictive information instead of tumor sampling. 12,13

Detection of Activating Estrogen Receptor Gene (ESR1) Mutations in Single Circulating Tumor Cells

“…Two hot spot mutations in codon 537 and 538 of ESR1 gene were investigated by digital PCR (dPCR). Those findings showed monitoring ESR1 mutations by dPCR was feasible, but not all mutations found in the metastatic biopsies were detected also in matched cfDNA [40]. In our study we used the analysis on cfDNA as a validation of the results found at the CTC level.…”

“…In both samples, the mutation detected was Y537S, positioned in exon 8 of the LBD domain of ER, as well as one of the most common mutations found in metastatic lesions. This mutation was present only in some of the CTCs from the same patient, highlighting the importance of single cell analysis instead of the previously pooling strategy [40,42]. …”

Molecular Diagnostics in Breast Cancer Routine Practice

“…25,26 Interestingly, these mutations have been demonstrated in blood providing a monitoring option. 27 Breast tumours of women naïve for endocrine therapy do not seem to harbour these mutations, suggesting either the clonal selection of very rare resistant primary tumour clones or their later acquisition under the pressure of endocrine treatments. 25 Relatively many patients develop polyclonal mutations.…”

Liquid Biopsy in Metastasized Breast Cancer as Basis for Treatment Decisions

“…Murtaza et al [38] demonstrated in their study on 6 patients with advanced ovarian, breast and lung cancers that a high incidence of specific ctDNA alterations is associated with acquired drug resistance: A truncating mutation in the gene coding for mediator complex subunit 1 (MED1) was found in an MBC patient with progressive disease following treatment with tamoxifen and trastuzumab, and a splicing mutation in the growth arrest-specific 6 (GAS6) gene was identified in the same MBC patient following subsequent treatment with lapatinib. Sefrioui et al [39] demonstrated that the mutation in the estrogen receptor 1 (ESR1) gene that is responsible for resistance to endocrine therapy in breast cancer patients can be traced in ctDNA and possibly predicts disease progression.…”

“…Beyond ctDNA detection in the plasma of cancer patients in order to monitor disease dynamics, some groups were able to trace ctDNA mutations relevant to anticancer treatment resistance [38,39,40]. Murtaza et al [38] demonstrated in their study on 6 patients with advanced ovarian, breast and lung cancers that a high incidence of specific ctDNA alterations is associated with acquired drug resistance: A truncating mutation in the gene coding for mediator complex subunit 1 (MED1) was found in an MBC patient with progressive disease following treatment with tamoxifen and trastuzumab, and a splicing mutation in the growth arrest-specific 6 (GAS6) gene was identified in the same MBC patient following subsequent treatment with lapatinib.…”