Federal officials on Monday gave the go-ahead to the proposed merger between Cigna, one of the nation’s largest health insurers, and Express Scripts, a major pharmacy benefit manager.

The $52 billion deal, announced last March, is one of two proposed transactions involving pharmacy companies before the Justice Department. Last December, Aetna, another giant insurer, announced its plan to join forces with CVS Health, the drugstore chain that is the main independent rival to Express Scripts, in a $69 billion deal.

The Justice Department continues to review the deal between Aetna and CVS, although the two companies are also expected to receive a green light soon.

These combinations of powerful health insurance companies with the country’s dominant pharmacy benefit managers are occurring as established players in the health care sector are frantically searching for ways to fend off potential interlopers like Amazon, whose tentative forays into the pharmacy business have already shaken up the industry.