CD274 and non-small cell lung carcinoma: Low-dose MEKi (trametinib) and anti-PD-L1 combined therapy in KRAS-mutant NSCLC enhanced tumor microenvironment and T cell infiltration, reduced Ly6Ghigh PMN-MDSCs (myeloid-derived suppressor cells, a type of immune inhibitory cells that mainly suppress natural killer cells and effector CD8+ T cells) in tumor tissue, and inhibited tumor cell proliferation, leading to tumor cell apoptosis.