ABCG2 and glioblastoma: Abemaciclib demonstrated the ability to penetrate the BBB due to its substrate for P‐glycoprotein (P‐gp) and BC resistance protein (BCRP), which are two efflux transporters on the BBB, and significantly extended survival in an orthotopic U87MG intracranial glioblastoma xenograft model [20, 23].