ABCG2 and neoplasm: Previous studies, based on transcriptomic analysis, showed an increased expression of ABCG2, ALDH1 and FGF1 stem cell markers in the pale region, when compared to the tumor mass [21], indicating the presence, in the infiltrating front of the tumor, of a glioma stem cell (GSC) population possibly responsible for tumor recurrence [22,23,24].