In syngeneic mouse models of colon cancer, ATRA, together with ionizing radiation or PDL1-blocking Ab, improved anti-tumor control compared with the respective monotherapies, as evidenced by a massive increase in pro-inflammatory TNFα+ iNOS+ macrophages and IFNγ+ CD4+ and CD8+ T-cells in the local tumor tissue and systemically. This evidence concerns the gene CD8A and colonic neoplasm.