Comment by geuis

Keto diets seem to have at least a positive anecdotal effect. Putting aside the cancer part, a strict adherence to the caloric restriction diet has general health benefits. Whether the positive health benefits impact the cancer itself is unknown. It may simply be that being healthier helps patients deal with the impacts of chemo and radiotherapy.

Also possible is that caloric restriction helps to put the body into a biology mode that helps to combat cancerous tissue.

There's no solid science behind any of this, but generally being healthier helps with any medical treatments.