Germany's Merck KGaA has struck a deal to buy U.S. biotech company SpringWorks Therapeutics for an equity value of $3.9 billion to add rare cancer therapies ahead of expected revenue losses linked to expiring patents.

Merck KGaA’s $3.9 billion deal to buy SpringWorks Therapeutics Inc. will expand the German conglomerate’s presence in the US at a time when many companies are seeking to increase investment in the country.

Germany’s Merck agreed to acquire U.S. biopharmaceutical company SpringWorks Therapeutics for around $3.9 billion, in a bid to expand its oncology and rare disease business.