Interestingly, P4 increases the expression of PIBF from 1 h to 24 h in U373 human astrocitoma cell line (now known as U251 glioblastoma cell line after a short tandem repeat-PCR genotyping) [10], indicating a differential hormone regulation of PIBF expression depending on cell context in human glioblastomas. This evidence concerns the gene PIBF1 and glioblastoma.