FGF2 and neoplasm: Some other challenges are (i) current culture conditions enrich the population of GSCs towards EGFR- and FGFR-expressing cells by adding EGF and bFGF supplements, which likely limit the original tumor’s heterogeneity; (ii) the lack of a blood–brain barrier and endothelial cells to mimic the brain vasculature, and absence of immune cells to mimic the tumor–immune cells interaction; and (iii) variability between assays hampers suitable high-throughput capabilities and may thus make them clinically unfeasible.