The six MRGs used in the prognostic model were ABCA3, CTGF, AMIGO2, PREB, EXOSC5, and FHIT. The expression of the first three of these was increased in metastatic compared with primary osteosarcomas, while the latter three were decreased, suggesting differential functions for these genes in the metastatic process. This evidence concerns the gene PREB and osteosarcoma.