Early trials of a "game-changing" class of drugs that harness the body's immune system have been found to extend survival in sufferers of some of the most deadly cancers. One in 10 patients expected to die of kidney cancer had a "complete response" to a combination of the drugs ipilimumab and nivolumab, meaning the tumour was eradicated.Forty percent of patients with incurable kidney cancer saw a significant reduction in the size of their tumours. Standard treatments achieve this in just 5% of cases.The findings will be presented to the European Society for Medical Oncology conference, in Copenhagen this week.Separate research on patients with head and neck cancer found a doubling in one-year survival among patients given nivolumab.After one year, 36% of patients were alive, compared with 17% of those not on the drugs.The class of drugs - called immunotherapy - was last year hailed as showing "spectacular" results against skin cancer and lung disease.All immune cells contain a switch that turns them off when they come across something that is not harmful.But cancer has also evolved to flick that switch, thereby avoiding the body's defences.Nivolumab, which is marketed as Opdivo, works by removing the switch so that immune cells can spot cancer cells and clear them out of the body...