LONDON, June 9 -- Every big drugmaker is running from the same clock, the day a blockbuster loses its patent and the revenue that came with it falls away. GSK's clock starts ticking in 2028, when its best-selling HIV medicine loses exclusivity. On Tuesday the British company answered it the way the industry usually does, by buying someone else's pipeline.

GSK agreed to acquire Nuvalent, a US-listed cancer-drug developer, for $10.6 billion in cash, its largest acquisition in more than a decade. The price, about $124 a share, is a 40 percent premium to where Nuvalent traded the day before, and the market took it at face value, sending the stock up roughly 39 percent. The terms were laid out on Tuesday morning and detailed in a filing with ...