CDK4 and neoplasm: To further explore the biological functions of circSORBS1 in vivo, we performed immunohistochemical experiments and found that the expression levels of the proliferation-related protein Ki67 and the cell cycle-related protein CDK4 were decreased and that the expression levels of the apoptosis-related protein BAX and the antimigratory/invasive protein E-cadherin were increased in tumour tissues stably overexpressing circSORBS1 (Fig. 3G–N).