In experiments with the combined application of phytochemicals and immune checkpoint inhibitors, we found that phytochemicals promote the efficacy of ICIs by down-regulating the expression of immune checkpoints or/and their ligands (e.g., PD-1/PD-L1), as well as by blocking the pathways associated with cancer progression (e.g., PI3K/AKT, EGFR) (Figure 3). Here, PDCD1 is linked to cancer.