But analysts say the potential prize is much larger – a $50bn a year market if the future pipeline of IO drugs realise their full potential. That’s because there are still substantial gaps to plug in the market, both for Merck and BMS and its international rivals playing catch-up, including AstraZeneca. Only around 25-30pc of patients have been responsive to the early IO treatments. They also haven’t been approved for every type of cancer, with lung cancer remaining the largest – and largely unmet – potential market opportunity, worth up to an estimated $10bn a year. It is also the biggest cancer killer, responsible for more than 1.6m deaths each year.