CD8A and colorectal cancer: 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).