Parasits and brain tumor

I was reading some thing about parasites, some parasites that usually inhabits in our digestive systems actually ends up in our brain and can cause a lot of issues. However, this reminded me of something. I have recently learned that brain tumor is very hard to treat because there is a blood barrier between brain and blood vessels. What if we can use the parasites (or borrow the way it went into the brain) to deliver cancer treatment drugs for brain cancel patients?