Bristol-Myers to Buy Celgene in $74 Billion Cancer-Drug Bet (3)

Bristol-Myers Squibb agreed to acquire Celgene Corp. in a record-sized $74 billion deal that will unite two drugmakers battling for advantage in a crowded market for innovative cancer treatments.

Both companies have faced investor wariness about their prospects in recent months. Bristol makes an immunotherapy drug called Opdivo that accounts for roughly a quarter of its sales but that has trailed a rival medication from Merck & Co. Celgene, meanwhile, has been looking for a follow-up for its blockbuster blood-cancer therapy Revlimid.

The proposed union of the two companies represents a big bet that combined mass will help overcome the ...