[ihnorton]

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

and more generally: 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.