Most tumors express ABCB1/P-gp in high levels [346], including schwannomas, meningiomas, low-grade gliomas (astrocytomas, pilocytic astrocytomas), and high-grade gliomas (GBMs, anaplastic astrocytomas, and anaplastic oligodendrogliomas) [66,346]. Here, ABCB1 is linked to central nervous system cancer.