Anthem will buy Cigna for about $54.2 billion, creating the largest U.S. health insurer by membership and accelerating the industry's consolidation from five national players to three. The proposed acquisition, the health insurance industry's largest, comes three weeks after Aetna Inc agreed to buy Humana Inc for $37 billion. Health insurers are finding it tougher to raise prices following the roll-out of President Barack Obama's healthcare law, while grappling with soaring expenses of medications including cancer drugs that can cost each patient more than $100,000 a year.