Just a few weeks after President Donald Trump’s December promise that prescription drug prices would plummet "fast and furious," Patricia Brown checked into a California clinic for an infusion of Merck & Co.'s blockbuster cancer drug, Keytruda.

When the bill arrived, the clinic's charge for a 400 mg dose dominated the page: $162,567.74.

Brown, an accomplished cook battling lung cancer, owed about $2,000.

But the six-figure charges to Brown and her insurance company show how quickly prices for cutting-edge medical treatments can balloon in the U.S. health care system. Someone has to pay: An employer, taxpayers, or regular people whose insurance premiums go up and up.

The price of Keytruda for Americans starts high and often heads higher. Merck lists Brown’s dose at an already steep $24,000. Then, depending on the insurer, the health-care provider and any number of middlemen, prices can rise.