HLA-E and neuroblastoma: Here, we have tested different soluble plasma/serum molecules, precisely: (i) sHLA-E and sHLA-F, two molecules belonging to HLA-class Ib family as sHLA-G, that was previously characterized in NB [4], (ii) B7H3, a glycoprotein belonging to the costimulatory B7 family, whose expression in NB tumors associated with worse EFS [8]; (iii) calprotectin, a calcium-binding protein of the S100 family, recently identified as specific marker for bone marrow-infiltrating NB cells [9], and (iv) chromogranin, characterized as surrogate biomarker for neuroendocrine tumors [10, 11].