Mr Carter, 91, is one of the latest beneficiaries of a new drug type which many scientists, medics and pharmaceuticals executives believe is destined to transform the treatment of cancer. Until recently, advanced melanoma would have been a near-certain death sentence. That has begun to change since the arrival of Keytruda, the drug by Merck of the US given to Mr Carter, and a rival product, Bristol-Myers Squibb’s Opdivo.