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BACKGROUND/AIM: Hypoxia is significantly associated with the development of drug resistance, and endocrine therapy is ineffective against hormone receptor (HR)-positive breast cancer in hypoxic tumor environments. Eribulin has a unique anticancer effect in breast cancer cells and improves tumor hypoxia by vascular remodeling. Therefore, we investigated the effect of eribulin on HR-positive breast cancer cells that were resistant to endocrine blockade. MATERIALS AND METHODS: We established hypoxia-resistant breast cancer cell lines by continuous culture in a hypoxic environment. Parental and hypoxia-resistant cell lines were treated with eribulin and/or tamoxifen, and estrogen receptor (ER)-, epithelial-mesenchymal transition-, and hypoxia-related gene and protein expression changes in each surviving cell line were assessed. In addition, proliferation was assessed after eribulin treatment in the parental and hypoxia-resistant cell lines. We also assessed the effect of eribulin in vivo using subcutaneous xenograft models. RESULTS: Hypoxia-resistant cell lines showed significantly decreased expression of epithelial and ER-related markers and exhibited a higher level of resistance to tamoxifen. Conversely, eribulin treatment increased epithelial and ER-related gene and protein expression in hypoxia-resistant cell lines and enhanced the anticancer effect of tamoxifen. In in vivo xenograft models, eribulin treatment of hypoxia- and tamoxifen-resistant tumors slightly induced the re-expression of ER. In addition, hypoxia-resistant tumors treated with eribulin tended to respond better to tamoxifen. CONCLUSION: Eribulin ameliorated the aggressive behavior caused by hypoxia and induced the re-expression of ER in hypoxia-resistant breast cancer cells. Eribulin treatment of HR-positive breast cancer may resensitize cells to hormone blockade.

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The thirteenth annual workshop of the European Network for Breast Development and Cancer (ENBDC) Laboratories Annual Workshop took place on the 28-30 April 2022 in Weggis, Switzerland and focused on methods in mammary gland biology and breast cancer. Sixty scientists participated in the ENBDC annual workshop which had not been held in person since 2019 due to the global COVID-19 pandemic. Topics spanned the mammary gland biology field, ranging from lactation biology and embryonic development, single cell sequencing of the human breast, and stunning cutting-edge imaging of the mouse mammary gland and human breast as well as breast cancer research topics including invasive progression of the pre-invasive DCIS stage, metabolic determinants of endocrine therapy resistance, models for lobular breast cancer, and how mutational landscapes of normal breast during age and pregnancy determine cancer risk. The latest findings from participating researchers were presented through oral presentations and poster sessions and included plenty of unpublished work.

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Endocrine therapy (ET) is one of a number of targeted therapies for estrogen receptor-positive breast cancer (BRCA); however, resistance to ET has become the primary issue affecting treatment outcome. In the present study, a predictive classifier was created using a DNA methylation dataset to identify patients susceptible to endocrine resistance. DNA methylation and RNA sequencing data, and the clinicopathological features of BRCA, were obtained from The Cancer Genome Atlas. Stringent criteria were set to select and classify patients into two groups, namely those resistant to ET (n=11) and sensitive to ET (n=21) groups. Bump hunting analysis revealed that 502 out of 135,418 genomic regions were differentially methylated between these two groups; these regions were differentially methylated regions (DMRs). The majority of the CpG sites contained in the DMRs mapped to the promoter region. Functional enrichment analyses indicated that a total of 562 specific genes encompassing these DMRs were primarily associated with 'biological progress of organ morphogenesis and development' and 'cell-cell adhesion' gene ontologies. Logistic regression and Pearson's correlation analysis were conducted to construct a predictive classifier for distinguishing patients resistant or sensitive to ET. The highest areas under the curve and relatively low Akaike information criterion values were associated with a total of 60 DMRs; a risk score retained from this classifier was revealed to be an unfavorable predictor of survival in two additional independent datasets. Furthermore, the majority of genes (55/63) exhibited a statistically significant association between DNA methylation and mRNA expression (P<0.05). The association between the mRNA expression of a number of genes (namely calcium release activated channel regulator 2A, Schlafen family member 12, chromosome 3 open reading frame 18, zinc finger protein 880, dual oxidase 1, major histocompatibility complex, class II, DP ß1, C-terminal binding protein 1, ALG13 UDP-N-acetylglucosaminyltransferase subunit and RAS protein activator like 2) and the prognosis of patients with estrogen receptor-positive BRCA and ET resistance was determined using Kaplan-Meier Plotter. In summary, the predictive classifier proposed in the present study may aid the identification of patients sensitive or resistant to ET, and numerous genes maybe potential therapeutic targets to delay the development of resistance to ET.

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Endocrine therapies targeting oestrogen signalling have significantly improved breast cancer management. However, their efficacy is limited by intrinsic and acquired resistance to treatment, which remains a major challenge for oestrogen receptor α (ERα)-positive tumours. Though many studies using in vitro models of endocrine resistance have identified putative actors of resistance, no consensus has been reached. We demonstrated previously that oestrogen non-genomic signalling, characterized by the formation of the ERα/Src/PI3K complex, is activated in aggressive breast cancers (BC). We wondered herein whether the activation of this pathway is also involved in resistance to endocrine therapies. We studied the interactions between ERα and Src or PI3K by proximity ligation assay (PLA) in in-vitro and in-vivo endocrine therapy-resistant breast cancer models. We reveal an increase in ERα/Src and ERα/PI3K interactions in patient-derived xenografts (PDXs) with acquired resistance to tamoxifen, as well as in tamoxifen-resistant MCF-7 cells compared to parental counterparts. Moreover, no interactions were observed in breast cancer cells resistant to other endocrine therapies. Finally, the use of a peptide inhibiting the ERα-Src interaction partially restored tamoxifen sensitivity in resistant cells, suggesting that such components could constitute promising targets to circumvent resistance to tamoxifen in BC.

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PURPOSE: Outcome data on hormone receptor positive (HR+), human epidermal growth factor receptor 2 (HER2) nonamplified (HER2-) metastatic breast cancer (MBC) treated with palbociclib after treatment with everolimus are lacking. The PALOMA-3 trial, showing benefit of palbociclib plus fulvestrant compared to fulvestrant alone in HR+HER2- MBC after progression while receiving endocrine therapy excluded women previously treated with everolimus. The objective of this study was to examine outcomes of HR+HER2- MBC with prior exposure to everolimus while receiving palbociclib-based therapy. PATIENTS AND METHODS: A retrospective, single-institute review was conducted of HR+HER2- MBC from January 2014 to November 2016 in patients treated with palbociclib after prior treatment with everolimus. Progression-free survival (PFS) was defined as the time from initiation of palbociclib to the date of progression as determined by the treating physician based on radiologic, biochemical, and/or clinical criteria. Response rates were determined on the basis of available radiologic data. Objective response rate (ORR) was defined as the rate of any complete or partial responses; clinical benefit rate (CBR) was the rate of complete response, partial response, or stable disease for at least 24 weeks. RESULTS: Twenty-three patients with a mean (range) age of 68 (42-81) years were identified. Kaplan-Meier estimate showed median PFS of 2.9 months (95% confidence interval, 2.1-4.2); ORR was 0 of 23 and CBR was 4 (17.4%) of 23. In the PALOMA-3 trial, median PFS, ORR, and CBR of palbociclib cohort were 9.5 months (95% confidence interval, 9.2-11.0), 19%, and 67%, respectively. CONCLUSION: There is a limited clinical activity of palbociclib combinations after progression with everolimus combination therapy. Further studies are necessary to confirm these findings.

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PURPOSE: Liquid biopsy using digital PCR (dPCR) has been widely used for the screening of ESR1 mutations, since they are frequently identified in the hotspot. However, dPCR is limited to the known mutations. Therefore, we aimed to analyze the utility of next-generation sequencing (NGS) to discover novel ESR1 mutations. METHODS: Whole exon sequencing of the ESR1 gene using NGS was performed in 16 primary and 47 recurrent tumor samples and 38 plasma samples from hormone receptor-positive metastatic breast cancer patients. Functional analyses were then performed for the novel mutations we detected. RESULTS: We identified no mutations in primary tumors and six mutations in five recurrent tumors, including three types of known mutations (Y537C, Y537N, and D538G) and two novel mutations (E279V and G557R). We also identified seven mutations in five plasma samples, including three types of known mutations (S463P, Y537S, and D538G) and one mutation not reported in COSMIC database (L536H). All nine patients with ESR1 mutations were treated with aromatase inhibitors (AIs) prior to sampling, and the mutations were frequently detected in patients who received AI treatments in the metastatic setting. Among the three novel mutations (E279V, L536H, and G557R), L536H, but not E279V and G557R, showed ligand-independent activity. All three mutant proteins showed nuclear localization and had no relation with non-genomic ER pathways. CONCLUSIONS: Although the molecular mechanisms of the E279V and G557R mutations remain unclear, our data suggest the utility of NGS as a liquid biopsy for metastatic breast cancer patients and the potential to identify novel ESR1 mutations.

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