It has been generally recognized that the abundance of CD8+ cytotoxic T cells in TME is associated with favorable clinical outcomes in various cancer types (Fridman et al., 2017); and corresponding biomarker utilizing the CD8+/CD3+ T cell density ratio has been validated to predict the risk of recurrence for colorectal cancer patients, independent from TNM staging information (Pagès et al., 2018). This evidence concerns the gene CD8A and cancer.