• PD-1 | Liver cancer Liver cancer, particularly HCC, has been a significant focus in the field of immuno-oncology due to the unique liver immune environment and the high prevalence of chronic liver diseases that predispose to cancer development. Liver immune tolerance is primarily regulated by various mechanisms, including the PD-1/PD-L1 pathway, which helps prevent autoimmunity but can also facilitate immune evasion by liver tumors. HCC cells and the surrounding stromal cells can express high levels of PD-L1. When PD-L1 binds to PD-1 on T cells, it inhibits T cell activation and proliferation, reduces cytokine production, and promotes T cell exhaustion. The liver's microenvironment is immunosuppressive, which helps in maintaining tolerance to various antigens. TAMs and other immune cells in the liver can express PD-L1, contributing further to the immunosuppressive milieu. Drugs that block the PD-1/PD-L1 pathway can restore T cell activity and enhance the immune system ability to target and kill cancer cells. The PD-1 | liver cancer concept pair is an example of co-occurring concepts that increased on an average at a modest rate (2-fold) over 2020-2022 while having a relatively high number of publications overall (Figure ) indicating that it is perhaps more well-established than the rest.