ESR1 and breast carcinoma: Overexpression of EGFR is frequently observed in ER− breast cancer, which in turn hyperactivates mitogen-activated protein (MAP) kinase (MAPK) signalling [44–46], which may induce loss of ER gene transcription and expression [42, 47], suggesting that UCHL1 regulates ER stability through EGFR stabilisation and subsequent MAPK hyperactivation.