PTGS2 and cancer: Although recent reports showed that PTGS2 was also implicated in chemoresistance of certain malignant tumors including liver, pancreatic, bladder, esophageal, and gastric cancers (Gee et al., 2006; Zhi et al., 2006; Harris, 2009; Mukherjee et al., 2009; Wang and Dubois, 2010; Wang et al., 2014; Liu et al., 2015a; Liu et al., 2017), and inhibition of PTGS2 effectively enhanced the sensitivity of tumors to drugs, the detailed mechanisms by which PTGS2 contributing to the development of chemoresistance remained elusive.