In the latest research on the treatment of liver cancer, it is found that the antitumor effect of TLR9 agonist combined with anti-PD-1 antibody or anti-PD-L1 is significantly better than single-agent therapy.346 The activation of TLR9 inherent in liver cancer cells regulates the autoarylation and ubiquitination of poly(ADP-ribose) polymerase-1 and the phosphorylation of STAT3, which together upregulate the expression of PD-L1 and eventually induce immune escape. This evidence concerns the gene PARP1 and liver cancer.