In the study, prognostic and predictive values have been examined of immunohistochemical studies on expression of four distinct proteins, linked either to sensitivity or to resistance of breast cancer cells to tamoxifen: oestrogen receptor alpha (ER), pS2 (Fitzgibbons et al, 2000), metallothionein (MT) (Surowiak et al, 2005b) and CD24 (Surowiak et al, 2006) in the group of 104 patients with invasive breast cancer. Here, ESR1 is linked to breast cancer.