This is interesting since tumor cells rely heavily on glucose (sugar or carbohydrate) metabolism. However, a ketogenic diet is a difficult one to maintain over time and we still do not have enough long-term data to say if there are other health benefits or hazards (in humans).
It is interesting to note that at an Aging Research Seminar I attended last week the consensus was a high carbohydrate diet increased the healthspan and lifespan. This was evident in a number of models.
Looks like we have a ways to go before we can cure or prevent cancer while simultaneously improve the healthspan and the lifespan of humans.