In PDAC (pancreatic ductal adenocarcinoma), the expression of VISTA may be associated with TLR4; the downregulation of VISTA and TLR4 by siRNA and naloxone, respectively, can inhibit the growth of PDAC, indicating that VISTA and TLR4, with their downstream signal pathways, are all involved in PDAC growth [83]. This evidence concerns the gene TLR4 and pancreatic ductal adenocarcinoma.