To this end, two MCF-7 cell clones stably expressing full length human ERβ (Ct- and Nt-ERβ cells), that represent a useful model to recapitulate in vitro the biological effects of this receptor subtype in hormone-responsive BC [10, 17-19], were used to perform smallRNA-Seq and compare piRNA expression with that of ERβ- wt MCF-7 cells under the same experimental conditions. Here, ESR2 is linked to breast cancer.