Researchers caution against seeing “immuno-oncology” as a miracle cure. Keytruda and Opdivo have so far been used mainly against melanoma and a type of lung cancer — and less than a third of people with those conditions respond to treatment. “There are still a number of very significant questions,” says Sir Harpal. “The most important is why only a relatively small population benefits. How can we pinpoint who will benefit and who won’t and why?”