In addition, our proof-of-concept demonstration of the therapeutic efficacy of PML pharmacological inhibition with ATO indicates that (1) repositioning of ATO (that is currently used in the treatment of acute PML) for BCa therapy is a viable approach, (2) there is strong support for the development of novel and more effective PML inhibitors and (3) the identification of combined therapies with PML inhibitors in BCa is a novel and exciting area of investigation. This evidence concerns the gene PML and progressive multifocal leukoencephalopathy.