The benefits of fasting for some types of cancer are well established, See:
medicalnewstoday.com/articl...
...but how effective is fasting for colon cancer?
I fast 68 hours every month, so, when I was told I had to eat no fibre before my colonoscopy, I told the medic I would fast... so I fasted for three days before the colonoscopy.
I had a haemorrhoid, and I thought that was why I had been producing D or crescent-shaped stools.
They found an adenomatous polyp, about 7mm in diameter, but well over halfway across the sigmoid... and my stools are now cylindrical - so the polyp must have partially blocked the sigmoid, and shrunk in response to the fast.
There have been anecdotal observations of tumours disappearing during a long (e.g. 21-day) fast... so, it is not surprising that an adenoma shrinks during a fast.
For information about (Intermittent) Fasting (IF), See: