PDCD1 and metastatic colorectal cancer: In particular, IC inhibitors (ICIs) targeting the programmed cell death protein-1/ligand-1 (PD-1/PDL-1) axis or cytotoxic T lymphocyte antigen 4 (CTLA-4), alone or in combination with further targeted- or chemo-therapies, have become the first-line treatments of numerous cancers such as advanced melanoma (Michielin et al. 2019), metastatic colorectal cancer (Morris et al. 2023), head and neck squamous cell carcinoma (Daste et al. 2024) and non-small cell lung cancer (Cortiula et al. 2022).