Updated from 7:57 a.m.

J.C. Penney (JCP) has earned the unfortunate distinction of being the lone department store to disappoint Wall Street with its third-quarter results. 

Shares of the mid-tier department store plunged as much as 9% in premarket trading as the third-quarter loss per share came in at 21 cents, worse than forecasts for a loss of 20 cents. Net sales tallied $28.6 billion, falling shy of Wall Street estimates for $2.95 billion. 

Here's what has Wall Street spooked about J.C. Penney. 

Same-store sales miss estimates.

Despite mall rival Macy's (M) showing improved sales trends in apparel during the quarter vs. earlier in the year, J.C. Penney wasn't so lucky. J.C. Penney's third-quarter same-store sales fell 0.8% compared to estimates for a 2.7% increase, in large part due to weakness in apparel.

The company's Chairman and CEO Marvin Ellison told analysts on a conference call that apparel sales were down in women's, men's and kids categories.

"We aren't pleased with the results in apparel," said Ellison, who was quick to highlight the impact of warm fall weather. Sephora cosmetics shops and home goods sold well, said J.C. Penney.

Morgan Stanley analyst Kimberly Greenberger said ahead of J.C. Penney's results, "Our September and October store checks [at J.C. Penney] revealed sluggish store traffic and elevated apparel clearance, suggesting underlying fundamentals remain soft."

On the positive side, J.C. Penney said its sales trends improved in October, thanks to momentum behind its new appliance business.

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