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.

"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.
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.