CTLA4 and neoplasm: In the microenvironment of PAs, ICIs can block immune checkpoints to prevent their inhibition and negative regulation of immune cells, including cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) and programmed cell death protein-1 (PD-1) on T cells or programmed cell death protein ligand-1 (PD-L1) on antigen-presenting cells and tumor cells (Fig. 2C) [59].