ESR2 and lung cancer: Estrogen receptor β (ERβ) is the primary ER subtype expressed in lung cancer; upon binding to estrogen in the cytoplasm, ERβ activates non-genomic signaling pathways, including PI3K/AKT/mTOR and RAS/RAF/MEK/MAPK pathways, promoting cancer cell proliferation and apoptosis evasion (9, 10).