In lung cancer studies, TMPRSS2 has been found to be one of the genes upregulated by androgen exposure in A549 cells and is a direct target of AR.[68] Estrogen (E2) (17β-estradiol) can activate several receptors, including the nuclear transcription factor estrogen receptor α (ESR1) and estrogen receptor β (ESR2). This evidence concerns the gene ESR1 and lung cancer.