Furthermore, we analyzed the inhibitory immune checkpoint genes such as programmed cell death protein 1 (PD-1), cytotoxic T lymphocyte protein 4 (CTLA4), lymphocyte activation gene 3 protein (LAG3), and T cell immunoreceptor with immunoglobulin and ITIM domain (TIGIT), which participate in T cell dysfunction and malfunction of anti-tumor immunity[29], and discovered that they were significantly up-regulated in the C1 cluster. Here, PDCD1 is linked to neoplasm.