Aetna and Humana Inc. said Thursday they would "vigorously" defend a planned merger against a Department of Justice lawsuit. The companies said that the merger has "tremendous value" to customers and thus "the facts do not support the basis for DOJ action." The $34 billion merger of Aetna and Humana, and a $48 billion deal for Anthem to buy Cigna, have encountered resistance from the Justice Department on grounds of reduced competition. All four companies' shares dropped amid reports of a planned Justice Department lawsuit. Humana shares dropped 17.1% over the last month, and Aetna stock dropped 3.2%, compared with a 4.0% rise in the S&P 500 .
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