NEW YORK - Aetna Inc., the largest U.S. health insurer, was sued Wednesday by a shareholder who says the firm should have accepted a $10 billion takeover offer from Wellpoint Health Networks Inc. and ING Groep NV.The shareholder, Barnett Stepak, alleged that Aetna and its directors breached their fiduciary duty to shareholders by rejecting the $70 a share offer, which was made in February. The suit, filed in a New York state court, seeks class-action status on behalf of all Aetna shareholders.

An Aetna spokeswoman did not immediately return a call for comment.

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