ESR1 and breast cancer: The expression of GPR30 in 50% of ER +  breast cancer patients,68 together with the overexpression of EGFR in acquired resistance suggests that Gβγ subunit protein of GPR30 may induce the GPR30/EGFR signaling cascade.74 The downstream ligand‐activated GPR30 signaling involves activation of SRC‐like tyrosine kinase and metalloproteinases leading to activation of the HB‐EFG which, in turn, activates the EGFR signaling pathway leading to cell growth in response to the phosphorylation of Erk1/2 kinases.74, 75