Keto forces your body to burn fat. At our age, your body may be so used to burning sugar that it will take rigid discipline to burn the fat.
Burning fat kills mutated cells. The more cells mutate, the less they can use fat and the more they have to use sugar. You rebuild your body with cells that are more close to the original if you stick to keto strictly after wearing it out.
You do have to eventually taper off. Cancer is when the cells become so mutated that they can invade other organs, but mutations can also cause local masses.