PDCD1 and neoplasm: We evaluated the immune checkpoint score based on immune regulatory molecules including Cd274, Ctla4, Havcr2, Lag3, Pdcd1, Pdcd1lg2, and Tigit. Consistent with the distribution of MDSC fraction, the primary tumor displayed the highest immune checkpoint scores in all groups, whereas the pre-metastatic liver showed the second highest scores (Figure 2A).