Shares in the healthcare industry fell the most on a modestly positive day for the broader U.S. equities complex.

France's Sanofi and Regeneron Pharmaceuticals said they would expand their longstanding alliance to jointly develop and market new immunology medicines, in a deal that could net the U.S. drugmaker up to $8 billion. The two companies have collaborated for more than two decades. Under the new agreement, Tarrytown, N.Y.-based Regeneron will receive $1 billion upfront from Sanofi and be eligible for additional payments of up to $7 billion subject to development, regulatory and commercial targets, the companies said.

Foghorn Therapeutics said it would be slashing nearly half of its workforce after scrapping a drug development partnership with Eli Lilly, forcing the biotech into defensive mode as it attempts to conserve cash.