The expression of syncytin-1 in the NB cell line SH-SY5Y was significantly increased in serum-free stem cell medium, and RNA analysis found that the overexpression of HERV was associated with the overexpression of the immune checkpoint molecule CD200 in NB tumors [96], indicating that serum-free stem cell medium promotes NB cell invasion [105]. This evidence concerns the gene CD200 and neuroblastoma.