RA can inhibit tumor cell proliferation in melanoma (Edward and MacKie, 1989; Zhang and Rosdahl, 2005; Li and Han, 2020) and promote immune surveillance in breast cancer, colorectal cancer, and melanoma by influencing the metabolism of MDSCs, upregulating genes related to immune response, and supporting the survival of tumor-specific CD8+ T cells (Guo et al., 2012; Paroni et al., 2020; Sun et al., 2020). This evidence concerns the gene CD8A and colorectal cancer.