"Not much of a suprise really. It fits the model that cancer cells are weaker, that any stress to the entire body might see them die off first"

I don't think that is the model ...

I think the idea is that the cancer cells are a luxury that your body supports because external queues indicate that it's living in the land of plenty. Why not support the energy needs of these extraneous cells ? There's plenty to go around ...

The fasting forces your body to act in a miserly fashion and like someone forced onto a budget, the extraneous luxuries are the first thing to go.

It's your body that starves the cancer cells.