ABCG2 and glioblastoma: For TMZ specifically, the inhibition of ABCB1, ABCG2, ABCE1, ABCC1, and ABCB5 has seen significant decreases in either GBM tumor volume/weight by (~40–90% reduction) [33,34,35,36,38,39,41,42,43], or significant increases in median survival (~1.3- to 5-fold increase) [34,35,42,43].