Sears Holdings Corp, once the largest U.S. retailer, warned on Tuesday about its ability to stay in business after years of losses and declining sales.<br /><br /> "Our historical operating results indicate substantial doubt exists related to the company's ability to continue as a going concern," Sears Holdings said in a filing with the Securities and Exchange Commission. Sears Holdings operates both Sears and Kmart stores.<br /> Sears shares, which hit an all-time low last month, tumbled more than 5 percent to $7.80 before the opening bell Wednesday. According to its most recent quarterly earnings, Sears lost more than $2 billion last year.
