BBC NEWS | Health | Gene switch can 'turn off cancer'

The really interesting part is that the cancerous cells return to acting like normal cells. Now obviously the tumour is still there, and as soon as you stop taking the drug it becomes cancerous again, but it is a pretty cool discovery. Although you would have thought that something that turns of Myc and stops the cancer cells from growing would stop the regular ones too. I guess they were lucky and doxycycline only disrupts the mutated gene. They don't talk about how it works. More information at New Scientist