There are some non-robot implementations of this kind of idea out there, including: http://en.wikipedia.org/wiki/Ibritumomab_tiuxetan http://en.wikipedia.org/wi

There are some non-robot implementations of this kind of idea out there, including: http://en.wikipedia.org/wiki/Ibritumomab_tiuxetan http://en.wikipedia.org/wiki/Ibritumomab_tiuxetan and more generally: http://en.wikipedia.org/wiki/Monoclonal_antibodies http://en.wikipedia.org/wiki/Monoclonal_antibodies tl;dr: use cancer-specific antibodies with a payload of a drug, gene vector, or radioactive particle (!) to very specifically kill cells.