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Breast cancers (BCs) typically express estrogen receptors (ERs) but frequently exhibit de novo or acquired resistance to hormonal therapies. Here, we show that short-term treatment with the anti-estrogens tamoxifen or fulvestrant decrease cell proliferation but increase BC stem cell (BCSC) activity through JAG1-NOTCH4 receptor activation both in patient-derived samples and xenograft (PDX) tumors. In support of this mechanism, we demonstrate that high ALDH1 predicts resistance in women treated with tamoxifen and that a NOTCH4/HES/HEY gene signature predicts for a poor response/prognosis in 2 ER+ patient cohorts. Targeting of NOTCH4 reverses the increase in Notch and BCSC activity induced by anti-estrogens. Importantly, in PDX tumors with acquired tamoxifen resistance, NOTCH4 inhibition reduced BCSC activity. Thus, we establish that BCSC and NOTCH4 activities predict both de novo and acquired tamoxifen resistance and that combining endocrine therapy with targeting JAG1-NOTCH4 overcomes resistance in human breast cancers.

Original publication




Journal article


Cell rep

Publication Date





1968 - 1977


Animals, Antineoplastic Agents, Hormonal, Basic Helix-Loop-Helix Transcription Factors, Benzazepines, Breast Neoplasms, Calcium-Binding Proteins, Cell Cycle Proteins, Cell Line, Tumor, Cell Proliferation, Drug Resistance, Neoplasm, Estradiol, Estrogen Receptor Antagonists, Female, Fulvestrant, Gene Expression Regulation, Neoplastic, Homeodomain Proteins, Humans, Intercellular Signaling Peptides and Proteins, Isoenzymes, Jagged-1 Protein, Membrane Proteins, Mice, Neoplastic Stem Cells, Proto-Oncogene Proteins, Receptor, Notch4, Receptors, Estrogen, Receptors, Notch, Retinal Dehydrogenase, Serrate-Jagged Proteins, Signal Transduction, Survival Analysis, Tamoxifen, Transcription Factor HES-1, Xenograft Model Antitumor Assays, p-Aminoazobenzene