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    BIOMARKER:

    ER positive

    i
    Other names: ESR1, Era, ESR, NR3A1, ER, ER beta
    Entrez ID:
    2099
    Related biomarkers:
    Expression
    Mutation
    CNA
    Fusion
    Others
    1d
    PROMISE: Genetic Analysis in Blood and Tumor Samples From Patients With Advanced or Metastatic Estrogen Receptor Positive and HER2 Negative Breast Cancer Receiving Palbociclib and Endocrine Therapy (clinicaltrials.gov)
    P=N/A, N=68, Active, not recruiting, Mayo Clinic | Trial completion date: Mar 2026 --> Mar 2028 | Trial primary completion date: Mar 2026 --> Mar 2028
    Trial completion date • Trial primary completion date • IO biomarker
    |
    HER-2 (Human epidermal growth factor receptor 2) • PD-L1 (Programmed death ligand 1) • ER (Estrogen receptor)
    |
    ER positive • HER-2 negative • HER-2 negative + ER positive
    |
    Ibrance (palbociclib)
    2d
    Testing Low Dose Tamoxifen for Invasive Breast Cancer, LoTam Trial (clinicaltrials.gov)
    P3, N=1556, Suspended, Alliance for Clinical Trials in Oncology | N=1156 --> 1556
    Enrollment change
    |
    HER-2 (Human epidermal growth factor receptor 2)
    |
    ER positive • HER-2 negative • HER-2 negative + ER positive
    |
    Prosigna® Breast Risk of Recurrence (ROR) Test • Oncotype DX Breast Recurrence Score®Test
    |
    tamoxifen • letrozole • anastrozole • exemestane
    2d
    Evaluating the investigational drug landscape for ESR1-mutated, estrogen receptor positive, HER2 negative metastatic breast cancer. (PubMed, Expert Opin Investig Drugs)
    Routine assessment of ESR1 mutations using liquid biopsy should be integrated into clinical practice to enable dynamic, molecularly guided treatment optimization. The expanding arsenal of ER-targeted therapies supports personalized sequencing strategies that move beyond rigid temporal cutoffs and improve outcomes in ET resistant disease.
    Journal
    |
    HER-2 (Human epidermal growth factor receptor 2) • ER (Estrogen receptor)
    |
    ER positive • HER-2 negative • ESR1 mutation • ER positive + HER-2 negative • HER-2 negative + ER positive • HER-2 negative + ER positive + ESR1 mutation
    2d
    Brain-selective estrogen therapy in male and female marmosets partially counteracts the adverse effects of aromatase inhibition on the brain and behavior. (PubMed, J Neurosci)
    We investigated whether DHED could prevent side effects associated with the aromatase inhibitor letrozole in a primate model of aging...Here, we show that a brain-selective estrogen therapy administered orally via the prodrug DHED substantially increases estrogen levels in the marmoset brain without affecting the periphery and normalizes impairments in working memory, hippocampal neuronal excitability and sleep induced by aromatase inhibition. These findings in a translational primate model represent a significant advance for women's health by positioning DHED as a non-invasive, safe and efficient novel hormone therapy to improve quality of life of women with ER+ breast cancers.
    Journal • Adverse events
    |
    ER (Estrogen receptor)
    |
    ER positive
    |
    letrozole
    3d
    Single-cell transcriptomics profiling elucidates RBP-driven metastatic signaling pathways in ER+ breast cancer. (PubMed, iScience)
    Functional perturbation experiments in ER+ breast cancer cells showed that TGF-β stimulation enhanced invasive behavior, whereas knockdown of MMP1 or COL7A1 attenuated epithelial-mesenchymal transition (EMT) marker expression and invasion. Together, our study delineates RBP-associated regulatory programs linking cellular state transitions to invasive signaling in ER+ breast cancer.
    Journal
    |
    ER (Estrogen receptor) • TIMP1 (Tissue inhibitor of metalloproteinases 1) • TGFB1 (Transforming Growth Factor Beta 1) • HSPA6 (Heat Shock Protein Family A (Hsp70) Member 6) • MMP1 (Matrix metallopeptidase 1) • KRT18 (Keratin 18)
    |
    ER positive
    3d
    CAAA603B12101: [177Lu]Lu-NeoB in Combination With Ribociclib and Fulvestrant in Participants With ER+, HER2- and GRPR+ Advanced Breast Cancer (clinicaltrials.gov)
    P1, N=48, Recruiting, Novartis Pharmaceuticals | Active, not recruiting --> Recruiting
    Enrollment open
    |
    HER-2 (Human epidermal growth factor receptor 2) • ER (Estrogen receptor) • PGR (Progesterone receptor)
    |
    ER positive • HER-2 negative • HER-2 negative + ER positive
    |
    Kisqali (ribociclib) • fulvestrant • goserelin acetate • AAA603
    3d
    PDZK1 disassembles HER2-HSP90 complexes to promote ubiquitin-mediated HER2 degradation and overcome therapy resistance. (PubMed, J Adv Res)
    PDZK1 functions as a regulator of HER2 stability and may serve as a potential biomarker and therapeutic target in HER2-positive breast cancer. Pharmacological upregulation of PDZK1 may represent a promising combinatorial therapeutic strategy for overcoming therapeutic resistance in breast cancer.
    Journal
    |
    HER-2 (Human epidermal growth factor receptor 2) • ER (Estrogen receptor) • HSP90AA1 (Heat Shock Protein 90 Alpha Family Class A Member 1Heat Shock Protein 90 Alpha Family Class A Member 1)
    |
    HER-2 positive • ER positive
    |
    Prosigna® Breast Risk of Recurrence (ROR) Test
    |
    tamoxifen
    4d
    PAK1 activation drives divergent resistance mechanisms to aromatase inhibition and tamoxifen in a luminal: A breast cancer model. (PubMed, Mol Oncol)
    In the tamoxifen resistance context, PAK1 inhibition induced activation of the pro-apoptotic protein BAD and triggered apoptosis while proliferation-related kinases were suppressed in the estrogen-deprived model. Our findings position PAK1 as a mediator of resistance to endocrine therapies suggesting that targeting PAK1 may present a novel strategy to overcome endocrine therapy resistance in ER+ breast cancer.
    Preclinical • Journal
    |
    ER (Estrogen receptor) • EGF (Epidermal growth factor) • PAK1 (p21 (RAC1) activated kinase 1)
    |
    ER positive
    |
    tamoxifen
    4d
    The clinical relevance of apocrine morphology in breast cancer depends on the estrogen receptor status. (PubMed, NPJ Breast Cancer)
    Conversely, in ER-positive tumors, apocrine morphology was associated with increased proliferation, enhanced immune-related signaling, and greater genomic instability. In conclusion, apocrine morphology represents an ER-dependent biological state with distinct prognostic and molecular implications.
    Journal
    |
    ER (Estrogen receptor)
    |
    ER positive • ER negative
    5d
    ONO-4578-06:Phase I Study of ONO-4578 and Letrozole Plus CDK4 /6 Inhibitors in Breast Cancer (clinicaltrials.gov)
    P1, N=46, Completed, Ono Pharmaceutical Co., Ltd. | Active, not recruiting --> Completed
    Trial completion
    |
    HER-2 (Human epidermal growth factor receptor 2) • ER (Estrogen receptor) • PGR (Progesterone receptor)
    |
    ER positive • HER-2 negative • PGR positive • HER-2 negative + AR positive + ER positive • HER-2 negative + ER positive
    |
    Ibrance (palbociclib) • Verzenio (abemaciclib) • letrozole • BMS-986310
    5d
    Testing Whether Hormone Therapy With Ribociclib is as Effective as Chemotherapy Followed by Hormone Therapy With Ribociclib for the Treatment of High Anatomic Stage Breast Cancer With Low Recurrence Risk, The RxFINE-Low Trial (clinicaltrials.gov)
    P3, N=1978, Recruiting, National Cancer Institute (NCI) | Not yet recruiting --> Recruiting | Initiation date: Jul 2026 --> Feb 2027
    Enrollment open • Trial initiation date
    |
    HER-2 (Human epidermal growth factor receptor 2) • ER (Estrogen receptor)
    |
    ER positive • HER-2 negative • ER negative • HER-2 negative + ER positive
    |
    Oncotype DX Breast Recurrence Score®Test
    |
    Kisqali (ribociclib) • letrozole • anastrozole • exemestane
    5d
    Palbociclib With Fulvestrant for Metastatic Breast Cancer After Treatment With Palbociclib and an Aromatase Inhibitor (clinicaltrials.gov)
    P2, N=60, Active, not recruiting, Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins | Trial completion date: Jun 2026 --> Dec 2026 | Trial primary completion date: Jun 2026 --> Dec 2026
    Trial completion date • Trial primary completion date
    |
    HER-2 (Human epidermal growth factor receptor 2) • ER (Estrogen receptor) • PGR (Progesterone receptor)
    |
    ER positive • HER-2 negative • HER-2 negative + AR positive + ER positive • HER-2 negative + ER positive
    |
    Ibrance (palbociclib) • fulvestrant