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.

Merck KGaA said the deal will grow its U.S. presence and expand the reach of SpringWorks’ drugs, including one approved in February.