I have heard some people having luck by switching to a ketogenic diet. Here’s a paper I could find on PubMed about this. Sorry to hear about your friend.

https://pmc.ncbi.nlm.nih.gov/articles/PMC9504425/

Edit: I am not a doctor. My wife is a physician and I spoke to her before posting this.

This. It is very dependent on the type of cancer. There is a lot of research on this. For a little context, I was a pediatric neurology professor for a while, and have been on a low carb diet for a decade. Much of the department did low carb, as did much of the oncology dept. Many kids with epilepsy are put on keto as well with great effect. I did a deep dive into low carb research before starting and keeping with the diet, and found a lot about using it for cancer therapy. I'm not sure what has changed in the last 10 years, but the above abstract looks promising. With a GBM, they probably don't have much to lose. *This is not medical advice, I'm not an MD (I was a BME doing epilepsy research), have them check with their Dr.

I wish I had something better to add, but I can add an anecdotal +1 to this.

A relative went keto pretty hard after a bad diagnosis and they are still going strong. As far as I understand it, cancer cells can only function on glucose.

+1 on this. I did my thesis on Glioblastoma-related imaging stuff [1]. The state of the art at the time (~2016) was that, realistically, none of the current treatments were "great", unfortunately. In short, you have 1) surgery, 2) chemotherapy, 3) radiation. Those treatments did extend survival in studies, but the overall survival of Glioblastoma patients was (tragically) still very bad at 12-24 months, and none of those therapy options were a cure.

As a side note, I recommend the book "Being Mortal" from Atul Gawande. The TLDR here is that our healthcare systems tend to overtreat patients, especially those with cancer who actually have a rather bleak prognosis, because it's easier for a physician to simply order all treatments and tell the patient "all good here, good luck" instead of taking the time to sit down and have a (long) conversation about the bleak prognosis and which options are actually still worth it. By "worth it" I mean that there are trade-offs to each treatment option, and it takes some very careful weighing whether each one provides a net benefit for your friend's individual situation. E.g. surgery might extend survival by X months, but might also create, worst case, new disabilities. So now you're faced with the very difficult decision of whether to potentially live for a shorter time with less disabilities, or for a longer time with more. There's no perfect answer, but having this sort of discussion is a good step which many patients unfortunately never take. I think this is a failure in our healthcare systems and maybe in the education of physicians.

Now, if I personally had a Glioblastoma, on top of the standard of care (surgery probably makes sense etc.), I think the ketogenic diet would currently be my best shot. Yeah, sure.. it's mostly only case reports so essentially anecdotal evidence, but it does look promising.

Good luck for your friend!

[1] https://scholar.google.com/citations?user=tinu7tYAAAAJ&hl=en

Thanks a lot, I hadn't seen this. I'll read through.

While we're thinking about it, Vitamin D3 and K2-mk-7 are known to be helpful in that regard.

If diet could stop cancer, we'd be done by now. I guarantee every cancer will mutate to overcome any change in diet you can throw at it.