PTGS2 and neoplasm: To further verify the role of COX2 in the development of acquired resistance to anti-PD-1 treatment, we knocked out COX2 in B16F10-R tumour cells (Figure 5A and Figure S6), and we found that PGE2 secretion was significantly reduced in B16F10-R-knockout tumours compared with B16F10-R tumours in vitro (Figure S7B).