TGIF1 and lung cancer: The aim of this study was to investigate the effect of CircCCND1 on the malignant biological behaviors of lung cancer cells by regulating the miR-340-5p/transforming growth factor β-induced factor homeobox 1 (TGIF1) axis.<h4>Methods</h4>The expression of CircCCND1, miR-340-5p, and TGIF1 mRNA in human normal lung epithelial cells BEAS-2B and human lung cancer H446 cells were detected.