CD274 and neuroblastoma: Immunohistochemical analysis of PD-L1 in a cohort of 51 NB patients further demonstrated pronounced expression in the NB-BBM group, with a tumor proportion score (PD-L1 protein-expressing tumor cells as a proportion of whole tumor cells) > 1 distinguishing metastatic and non-metastatic NB patients (P = 0.046) (Fig. 5G, H).