HCAR1 and pancreatic neoplasm: Radiotherapy enhances the Warburg effect in pancreatic cancer cells, resulting in a sustained increase in lactate secretion; but lactate can lead to significant up-regulation of phosphorylated STAT3 in MDSCs via the G protein-coupled receptor 81/hypoxia-inducible factor-1α pathway, and MDSCs are activated, promoting the development of an immunosuppressive microenvironment in pancreatic cancer, leading to resistance to radiotherapy [71].