Beneficial GM Parasites

Is it feasible that we could genetically modify parasitic organisms to compel them to devour unwanted materials in the human body, like cancer cells or cholesterol?

There’s talk of medical ‘nanobots’ which could float around the human body doing good, but as parasites are well-practiced at bodily navigation that seems to be half the battle won.

If not GM organisms, how about chip-controlled tapeworms to investigate the bowel?