PPBP and neoplasm: Among the genes significantly up-regulated in the BM-infiltrating GD2 positive cells compared to primary tumor cells (Table 1 and Table S2) several genes were commonly expressed by various lineages of BM resident cells, namely: i) cathelicidine (CAMP), myeloperoxidase (MPO), myeloid cell differentiation antigen (MNDA), CD177, FC receptor, CD69 expressed by myelo-monocytic cells; ii) mu chain, CD19, and BLK expressed by B cells and iii) IL-1β, IL8, and CXCL7 (PPBP) expressed by several hematopoietic and mesenchymal cells.