CD28 and cancer: These results showed that the five prognosis-related cancers—KIRC, SKCM, STAD, TGCT, and UCEC—were highly positively correlated with the six immune checkpoints—inducible T-cell costimulator (ICOS), cytotoxic T lymphocyte-associated molecule 4 (CTLA4), CD28, CD80, PDCD1LG2, and CD86 (r > 0, ∗∗∗p < 0.001) (Figure 3F and Table 1).