Activating the immune system at the site of a tumor can re-engage the immune system.
A number of years back, there was a great deal of excitement about using viruses to target cancer. A number of viruses explode the cells that they’ve infected in order to spread to new ones. Engineering those viruses so that they could only grow in cancer cells would seem to provide a way of selectively killing these cells. And some preliminary tests were promising, showing massive tumors nearly disappearing.