Estrogen receptor (ER)–Human epidermal growth factor receptor 2 (HER2) signaling axis (ER–HER2 axis)

The Estrogen receptor (ER)–Human epidermal growth factor receptor 2 (HER2) signaling axis is a critical regulatory network in breast cancer characterized by bidirectional crosstalk between the ER and HER2 pathways (Arpino et al., 2008, Breast Cancer Research). In this axis, HER2-mediated activation of downstream cascades, such as the MAPK and PI3K/Akt pathways, can lead to the phosphorylation and activation of ER and its coactivators, allowing for estrogen-independent tumor growth and survival (Schiff et al., 2004, Journal of Clinical Oncology). Conversely, ER signaling can transcriptionally regulate the expression of HER2 and other EGFR family members, creating a feedback loop that promotes therapeutic resistance (Giuliano et al., 2011, Clinical Cancer Research). This interaction is a primary mechanism of resistance to endocrine therapies like tamoxifen, as the tumor cell can bypass ER inhibition by upregulating growth factor signaling. Clinical management of tumors driven by this axis often requires a "dual blockade" strategy, using combinations of endocrine agents and HER2-targeted therapies to effectively shut down both survival pathways and improve patient outcomes (Johnston et al., 2009, Journal of Clinical Oncology).

Other names

ER/HER2 crosstalkER-HER2 bidirectional signalingEstrogen receptor-ERBB2 axisER-HER2 pathway

The therapeutic mechanism involves the simultaneous inhibition of the genomic and non-genomic actions of the Estrogen Receptor (ER) and the kinase activity or dimerization of the HER2 receptor. This dual blockade disrupts the bidirectional crosstalk where HER2 signaling activates ER in a ligand-independent manner and ER signaling upregulates HER2 pathway components (Arpino et al., 2008, Breast Cancer Research). By targeting both nodes, therapies aim to overcome endocrine resistance and prevent the activation of alternative survival pathways (Schiff et al., 2004, Journal of Clinical Oncology).