That's a interesting question and I think I will looks this up in more detail over the weekend, but for now I have this:

As far as I know this subject is still unclear. While autophagy would hinder cancer cells in early stages it also would help in later stages when the tumor gets bigger and the cells need more energy than can be provided (because blood vessels have to grow first). But that seems to differ from cancer type to cancer type, as far as I found (just a quick surface search for now).

There are some studies trying to find how to use autophagy to treat cancer.