ESR1 and breast cancer: To further confirm the association of CCKBR/ERK/P65 and ER positive BC, the levels of CCKBR, p-ERK and p-P65 in fresh tumor and corresponding adjacent normal BC tissues (N = 5) were determined by western blot and IHC (ER, PR and HER2 status was determined in Additional file 2: Figure S1).