Tim Ferris' Tools of Titans has a section from a doctor (not oncologist) who recommends fasting the days before chemo treatment. Supposedly it sensitizes the cancer cells to the chemo. I'm hesitant to give advice to cancer patients on the internet but there's more recommendations (in my book it's pg. 32-33). He also mentions keto diet, exogenous ketones, metformin, dichloroacetic acid, and finally hyperbaric oxygen, rapamycin in "modest, intermittent doses" and finally sequencing the tumor to see if a checkpoint inhibitor could be effective.

Again, recommendations from a health guru book and not an actual doctor, that I'm just copying here in case it helps. I have no experience with cancer other than a close relative passing away when I was much younger.