CD44 and lung adenocarcinoma: It was found that PM2.5 exposure (once per week for 6 weeks) promoted tumorigenesis and metastasis in lung adenocarcinoma in the xenograft, as well as the migration and invasion of lung adenocarcinoma cell lines [106], though downregulation of miRNAs (miR30a, miR125a, miR200a, miR200c, miR221, Let7C) and increased gene expression of fibrotic and inflammatory factors (including N-Cadherin, Fibronectin-1, Vimentin, Snail1, Slug, Zeb1, Zeb2, CD44, Abcg2, CD133) [106].