PTGS2 and neoplasm: Recent studies have reported that COX‐2 and the downstream prostaglandin E2 (PGE2) play a role in regulating the abundance and function of immune cells, such as CD8+, CD4+ T cells, and Treg cells, leading to tumor cell evasion of host antitumor immunity.[8] In addition, COX‐2 and downstream PGE2 also drive constitutive Indoleamine 2,3 dioxygenase 1 (IDO1) expression in human tumors and subsequently mediate intrinsic immune resistance.[9] Therefore, the COX‐2 inhibitor is an ideal PDT synergistic therapeutic agent for tumor treatment via PGE2 and IDO1 inhibition.