It is a moment of celebration for those battling against cancer. An experimental treatment that harnesses the body's own defences has shown extraordinary success for patients deemed incurable. The numbers are astounding - 94% of participants in one leukaemia trial saw their tumours vanish. In one study, beneficial effects lasted up to 14 years. And don't forget, this would have been a last resort.The patients in the trials had been failed by chemotherapy and every other available treatment. Most had less than five months to live. The intervention snatched them from the jaws of death.While "immunotherapy" - using our body's immune cells to attack tumours - isn't new, the effect in humans has never been this dramatic. Scientists, a famously pessimistic breed, have branded it a "real revolution". This is a joyful moment, one we should celebrate unreservedly.It could even be on a par with the sort of medical innovations we learnt about at school - Edward Jenner vaccinating a young boy against smallpox using cowpox pustules in 1796, for example. We have been obsessed with curing advanced cancers for 50 years and we may finally have a silver bullet.The truth is, however, that the next great challenge for scientists may have nothing to do with curing disease. It may offer no breakthrough moment like this. But it is something the vast majority of us will face as a result of myriad medical breakthroughs: old age.In the developed world, we are far more likely to have to deal with this condition than face life-threatening infections.Even those illnesses we do associate with old age, such as cancer and Alzheimer's, may be eliminated in the coming decades. The problem will therefore be one of coping with a massive healthy but frail, elderly population that needs care.New figures show how we are already failing at this task. The numbers show a 5% rise in death rates in England and Wales last year - the highest jump since World War 2.It is symptomatic of our inability to care properly for the old: in the UK more than 154000 people were stuck in hospital because they didn't have the necessary support at home.But if resources are the problem, technology may soon be able to help. Advances such as cheap ambient sensors and internet-connected bracelets or pendants could instantly connect older people with emergency services or carers.In Japan, where one in four people are over 65, empathetic humanoid robots are touted as the cheap, infinitely patient alternatives to human care workers, resulting in big savings for the government.A robot that is already on sale can recognise emotions such as sadness and joy, and lead the elderly in exercise.Big companies, including Panasonic and Toyota, are also testing androids that can perform tasks such as fetching water or closing the blinds.A cure for cancer may see unprecedented numbers reach their dotage. Once there, robotic "exoskeletons", which act as strength-enhancing mechanical limbs, may allow them to lift heavy objects with ease.However we tackle it, the bottom line is that we need to confront our own frailty. There is no point in defeating disease if our new lease of life is a misery. ..