PDCD1 and malignant colon neoplasm: In addition, according to the single-cell sequencing data from colon cancer (Lee et al., 2020), breast cancer (Kim et al., 2022), and stomach cancer (Kang et al., 2022), we found that the level of NKG2A expression in intratumoral cytotoxic T and NK cells was comparable to that of PD-1.