To confirm that PGE2 acts on NK cells via EP2 and EP4, the cells were cultured in thyroid cancer cell supernatants in the presence or absence of the EP2 antagonist AH6809 (20 μM) and/or the EP4 antagonist AH23848 (20 μM) (each at 10 μM) to block EP receptor signaling. This evidence concerns the gene PTGER4 and thyroid cancer.