(Wall Street Journal) – A dispute over a microscopic enzyme is threatening Merck & Co. plans to sell a new version of Keytruda, the cancer drug that generates nearly half of the company’s sales.

Merck has been tweaking Keytruda to make it easier to use—and to protect billions of dollars in revenue the company could lose after U.S. patent protection runs out in 2028 and rivals can begin selling copycats.

The enzyme in the new Keytruda allows it to be injected, rather than given intravenously. It is the subject of a brewing patent dispute between Merck and a biotech called Halozyme Therapeutics. (Read More)