POU4F2 and cancer: EVs exclusively contained PLEKHG2 (nucleotide-binding protein), GPR68 (a proton sensing G protein-coupled receptor 68), POU4F2, ADAMTS9, and Let-7 microRNA precursor, which are involved in cell development, signal transduction, and cancer metastasis (Schaefer et al., 2009; Shurtleff et al., 2017; Valadi et al., 2007).