They need to find a way to target only the tumor cells and not have the side effects on the normal cells. There is a lot of research going on to accomplish this with other treatments, such as antibody drug conjugates, convection enhanced delivery, super selective intraarterial intracranial infusion, gene therapies such as used by Tocagen and a few others.
Pathway linked to slower aging also fuels brain cancer
www.sciencedaily.com/releases/2016/12/161206103526.htm