ESR1 and breast neoplasm: To study these in vitro observations in a biologically and clinically relevant context in which ERα is present and the function of estrogen-responsive pathways was targeted by anti-estrogen treatment, we specifically examined microarray expression data from 69 ERα-positive breast tumors from patients belonging to a previously described cohort [37,38] from Uppsala, who had received adjuvant tamoxifen therapy following surgery (see Materials and methods).