Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

Investors suffered through a fourth day of losses for the broad market, as both the Dow and S&P didn't manage to avoid modest declines despite having bounced back from much larger pullbacks earlier in the session. Yet with the Dow and S&P 500 falling less than 0.2% and the Nasdaq actually rising slightly on the day, the huge declines for Express (NYSE:EXPR), Ambit Biosciences (NASDAQ: AMBI), and Thompson Creek Metals (OTC:TCPTF) stood out among the market's losing stocks.

Express dropped by 23% after giving negative guidance in its quarterly earnings report. Even though the retailer posted reasonable gains in sales and earnings for the third quarter, Express reined in its full-year earnings expectations, cutting its expected range by $0.06 to $0.09 per share. The retailer's comments only emphasize the extent to which promotional discounting has become more prevalent than ever, pointing to the likelihood that results for the holiday quarter throughout the industry won't manage to achieve hoped-for levels.

Ambit plunged 33% following bad news concerning its acute myeloid leukemia drug prospect quizartinib. The company announced that the FDA chose not to allow it to file for approval based solely on its trial data from phase 2 and 2b studies, instead requiring it to run a more costly and time-consuming phase 3 trial before considering a new drug application. Even though the company has substantial cash reserves to sustain it as it runs the study, investors nevertheless weren't happy with the delay.

Thompson Creek posted a nearly 10% decline, falling to a new low as analysts at TD Securities kept their negative rating on the mining company and again called for the stock to drop substantially from current levels. With the company seeing substantial amounts of debt coming due in the next four to six years, Thompson Creek needs to see prices of molybdenum return to higher levels in order to help support its debt repayment. Moreover, with its Mt. Milligan exploration project not yet having proven itself -- especially with gold and copper prices depressed -- Thompson Creek could have trouble making enough money to avoid hugely dilutive measures in the future.

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