SERPINE1 and glioblastoma: Validation of the functional effects of genes identified as associated with the infiltrative phenotype of invasive GBM cells was undertaken, using SERPINE1 as an example of a candidate gene consistently upregulated in 5-ALA/FACS-positive cells from the invasive region compared to the unsorted mixed population from the invasive regions (t-test P = .006) and 5-ALA/FACS-negative cell populations (t-test P = .014; Figure 4G).