ESR1 and breast cancer: Moreover, using the cBioPortal [23] to analyze the TCGA PanCancer dataset [21] and CPTAC [22], we were able to confirm that BiP mRNA and protein levels are associated with PAM50 breast cancer molecular subtype and the three immunohistochemical markers used in breast cancer diagnosis (ER, PR, and HER2), with them being higher in HER2+ and triple-negative breast cancer.