they're made by merck, bristol-myers, and roche which just got its drug fda approved last month. merck's medicine was used to treat jimmy carter's stage 4 melanoma. carter announced recently he was cancer free. >> it releases the brakes on the immune system andne permits the immune system to seek out and destroy tumors. it's exactly what was observed in the case of jimmy carter. what's remarkable and what we're seeing here at this meeting is that it seems to be active across a very, very broad range of tumors. nearly all. we're seeing that in a whole variety of different settings, very exciting. >> reporter: competition among pharmaceutical companies is only intensifying. with astrazeneca, pfizer, and others bringing their own version through clinical trials. >> a key question as many of these therapies enter the market is their price. as carry finds a way of escaping one drug, many see combinations of medicine as the future of treatment. with many medicines costing more than $1,000 a...