ESR2 and lung adenocarcinoma: ESR1 expression has been found to be higher than ESR2 in human lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC), suggesting that ESR1 may play a major role in inducing lung cancer (LC) cells.[69] However, in another study, exposure to TGF-β1 in bronchial epithelial cells resulted in dose-dependent and significantly reduced ESR1 and ESR2 mRNA and protein expression.[70] Therefore, whether ESR1 has a protective or inducing effect on pulmonary fibrosis is controversial.