POSTN and glioblastoma: Furthermore, we show that the extracellular protein POSTN (periostin, osteoblast specific factor, HGNC:16953), that has been shown to play a role in glioblastoma carcinogenesis and is an important factor in metastasis, is transcriptionally activated by p73, and that this activation leads to increased cell invasion of glioblastoma cells in vitro.