fasting can rid the body of tumors and cancer generally via , as long as it hasn't metastasized or spread to other parts of the body. It will also depend on the stage of cancer and where fasting is of little benefit in late-stage cancer.
In my opinion you are best to fast for 3 to 5 days on water-only according to thirst, and then an equal number of days on fresh live juices and then repeat the cycle: especially the cruciferous vegetable juices which are extremely effective at fighting and preventing cancer.