The notion that increased ABCB6 function plays an important role in enhanced ALA-PpIX levels in tumor cells is supported by the findings that human glioma tissues with higher ALA-PpIX fluorescence exhibit higher ABCB6 expression than glioma tissues with lower PpIX fluorescence, and ABCB6 overexpression significantly increases ALA-PpIX fluorescence in glioma cell lines [50]. This evidence concerns the gene ABCB6 and central nervous system cancer.