GPER1 and breast cancer: Firstly, it is required the GPER-activation for survival of xenograft-derived cancer stem cells and progression to metastatic disease, secondly, GPER leads to EGFR spread, transactivation, and responsiveness to growth factors as a result of their signaling, finally, patient outcome and treatment-response of breast cancer-affected patients are most hopeful in GPER negative cancers13–17.