MAPK1 and neoplasm: PD-L1 was previously shown to regulate the activation of ERK1/2 by binding with RAS, which consequently affects EMT of tumour cells.32 Additionally, the activation of STAT1/3 can be mediated by ERK1/2.44–50 These findings are consistent with our results, which suggest that there is a positive feedback loop between PKD3 and PD-L1 that drives EMT via ERK/STAT1/3 signalling, ultimately promoting tumour growth and metastasis (Fig. 8).