About 15 years ago, cancer researchers noticed a trend. Some of the patients they were following had advanced tumors but were surviving a surprisingly long time with an experimental treatment. One of the things they had in common was a specific type of antibody, which seemed to give the immune system a leg up.
That was noteworthy, because many cancer treatments depend on how tumors and immune cells fare as they face off in an elaborate game of cat-and-mouse. Normally, a cell in distress will display a protein on its surface, a kind of chemical alarm, flagging down the immune system like an orange spray-paint X marking a diseased tree for removal. The same is true of cancer cells: Their DNA damage makes them prime targets for culling. But many evolve to shed those alarm molecules, which helps them escape the immune system’s notice.