SAN FRANCISCO, United States — Gap Inc. shares plunged as much as 15 percent in late trading after the apparel chain posted disappointing results, a sign the company's much-vaunted springtime comeback hasn't materialised.Same-store sales — a key benchmark — dropped 7 percent in April, the San Francisco-based retailer said in a statement Monday. Analysts had predicted a gain of 1.1 percent, according to Retail Metrics. Preliminary earnings ranged from 31 cents to 32 cents a share in the first quarter, well below the 44 cents estimated by analysts.Chief Executive Officer Art Peck, who took the reins last year, had said the company would show signs of a turnaround by this season. Instead, sluggish store traffic in March continued into April. The company's budget-minded Old Navy fared especially poorly last month. Comparable sales at that chain plunged 10 percent in April, compared with the 2.6 percent increase analysts had estimated.Shares of Gap, the biggest U.S. apparel-focused retailer, fell as low as $18.47 in late trading after the results were released. They were already down 12 percent this year before the report.Reviewing StoresThe company also said it's evaluating its Banana Republic and Old Navy chains to find ways to be more efficient, especially outside of North America. It will give more details when Gap reports its final first-quarter results on May 19.“Our industry is evolving and we must transform at a faster pace, while focusing our energy on what matters most to our customers,” Peck said in the statement. “We are committed to better positioning the business to recapture market share in North America and to capitalizing on strategic international regions where there is a strong runway for growth.”By Lindsey Rupp; editor: Nick Turner.