NCAM1 and neuroblastoma: Whereas in unprocessed BM samples from healthy individuals GD2 expression is absent [23], in BM samples from stage 4 NB patients GD2 positive cells represented about 20–30% of mononuclear cells and 100% of these cells always co-express NB specific markers, as p75, CD56, and B7H3, thus confirming that the GD2-positive BM-infiltrating cells were indeed metastatic NB cells.