Merck & Co's cancer drug Keytruda, which works by boosting the immune system but has yet to be licensed in Europe, is the first medicine to be made available to patients in Britain under a new early access scheme. The Medicines and Healthcare Products Regulatory Agency said on Wednesday that the treatment had been cleared to treat adults and children from 12 years of age with advanced melanoma, the deadliest form of skin cancer, after other drugs had failed.