Multi-walled carbon nanotubes can be injected into a tumour. A low-power laser is then used to make the tubes vibrate which generates heat, which kills the tumour cells. William H. Gmeiner, group leader of the Wake Forest University School of Medicine lab that carried out the work said that the DNA used to coat the nanotubes helped prevent clumping of the tubes, which allowed more efficient energy transfer from the laser to heat up the nanotubes.
Here is a little more information from the Biocompare site.
The authors point out that toxicity studies will need to be carried out before moving the study from mice to man.
There are papers that suggest that multi-walled carbon nanotubes may present similar health hazards to asbestos fibres, due to their relative length and diameter.