During immune-tumor interactions, immune-cells may acquire tumor-specific molecules, including tumor antigens, checkpoint molecules (e.g., PD-1, PD-L1) (Hasim et al., 2022; Gary et al., 2012; Kawashima et al., 2021) or other surface markers, providing a molecular fingerprint of recent antigen engagement. This evidence concerns the gene PDCD1 and neoplasm.