PTGER1 and neoplasm: CAFs have been shown to produce prostaglandin E2 (PGE2), which not only stimulates the proliferation of HNSCC tumor cells, inhibits apoptosis, and determines the development of immunosuppression in the TME but also activates the invasive properties of tumor cells through interaction with receptors (EP1, EP2 and EP3) expressed by tumor cells [136,137].