For signaling proteins and interactions that are less studied or that were more recently identified as key players in these pathways, we also use interactions and information from other cancers and biological processes, and when available, focus on the consensus between experiments done on canonical cell lines, in particular, MCF7, T47D, and MDA-MB-415 for ER+ breast cancer, and BT474, JIMT1, HCC1954, SKBR3, and HER2-overexpressing MCF7 for HER2+ breast cancer. The gene discussed is ESR1; the disease is breast cancer.