PDCD1 and metastatic malignant neoplasm: The existence of S100A9 positive macrophages in tumor tissues, a key gene in the growth and metastasis of HCC, was related to the shorter survival time and the poor treatment of PD-1 antibody in metastatic cancer patients (Duan et al., 2018; Kwak et al., 2020; Wei et al., 2021).