Whole or myeloid Ffar2 gene deletion markedly inhibited urethane-induced lung carcinogenesis, Lewis lung carcinoma (LLC), and B16F10 melanoma tumor growth, through restricting MDSCs mediated L-Arginine consumption and promoting CD8+ T cell infiltration as well as anti-tumor response in the tumor microenvironment which benefit the outcome of cancer immunotherapy significantly. The gene discussed is CD8A; the disease is neoplasm.