To further validate the robustness of the ligand–receptor interactions linked to HCC prognosis, we evaluated the top two pairs, i.e., LGALS9-SLC1A5 and SPP1-PTGER4, representing the tumor-TAM communications for proof-of-principle analysis (Fig. 7a), as validation of all significant pairs would be technical challenging. The gene discussed is PTGER4; the disease is hepatocellular carcinoma.