S2 cells had no measurable BCAT1 mRNA transcript or protein and yet had a doubling time that was similar to A11 cells and both had similar growth rates in vivo as xenografts.16 Single-cell RNA sequencing has also shown a subset of glioblastoma cells with very low BCAT1 expression.23 Unlike A11 cells, BCAT1 expression was not induced in S2 cells by hypoxia, although they have functional HIF-1α since overexpression of BCAT1 upregulated a transcriptional target of HIF-1α, CAIX, and they have a functional BCAT1 gene since ectopic expression of c-Myc drove expression of functional enzyme. This evidence concerns the gene CA9 and glioblastoma.