A decade ago, US pharmaceuticals company Merck paid $41bn to acquire Schering-Plough, consolidating and cutting thousands of jobs amid an industry crisisof innovation and confidence. The companies touted their cholesterol and HIV treatments, briefly noting a “promising pipeline” in oncology.

Hidden in that pipeline was Keytruda, an antibody that enables the body’s immune system to attack cancers. It was an accidental acquisition, initially ignored by Merck and almost discarded but now its main blockbuster, with sales expected by JPMorgan to hit $16bn a year by the mid-2020s. It extends patients’ lives longer than chemotherapy alone, albeit expensively.

Rapid innovation in oncology drugs such as Keytruda and genetic medicine has prompted another merger wave. Bristol-Myers Squibb agreed to acquire Celgene for $90bn in January, GlaxoSmithKline agreed to buy the US biotech Tesaro for $5.1bn in December, and Eli Lilly said last month it was acquiring Loxo Oncology for $8bn.