I can vouch for that as far as Basal Cell Skin Cancer goes. Mine spread after biopsy and mohs surgery. The zapper eliminated every lesion.
Before using the zapper (ParaZapper MX), I tried several different therapies. I found that fasting would significantly reduce tumor size and might have eliminated the cancer in the long run. I did not want to wait.
This however, was only my experience and was not a FDA approved study. So there :^)