Where is your relative living? Typically the university hospitals have the best experts, ie UCSF and Stanford in the SF Bay Area (although for a GBM, I'd recommend UCSF). There are various ranking sites that list the best hospitals and in my experience, they're a good place to start.
I know it feels productive to start reading as much as you can about the disease pathology and treatments, and it won't hurt to be more informed, but for a stage IV GBM, your time would be much better spent trying to get hooked up with the best docs in the country. It's a terrible thing to deal with and some doctors have spent decades immersed in the research and literature -- let them be the experts but make sure you find someone who can give your relative a chance.
I know it feels productive to start reading as much as you can about the disease pathology and treatments, and it won't hurt to be more informed, but for a stage IV GBM, your time would be much better spent trying to get hooked up with the best docs in the country. It's a terrible thing to deal with and some doctors have spent decades immersed in the research and literature -- let them be the experts but make sure you find someone who can give your relative a chance.