Stocks finished narrowly lower on Tuesday, as investors seemed content with the impressive gains they've scored so far this month after a terrible January. Yet even though broad market benchmarks fell only a fraction of a percent, much larger losses hit shares of SINA (NASDAQ:SINA), VIVUS (NASDAQ:VVUS), and Tenet Healthcare (NYSE:THC) today due to company-specific news affecting their respective businesses.

SINA fell 9% after the company's quarterly earnings report prompted pessimism from investors and a price-target drop from analysts at Maxim Group. Sales grew by 43%, with impressive gains in both advertising and non-advertising revenue from SINA's key Weibo microblogging service. Yet growth in the number of average daily users of the Weibo service climbed by just over 4% from the third quarter, indicating slowing interest and increased competition from rival services. With no comments on speculation that SINA might make a public offering of shares of Weibo directly, investors didn't hear what they'd wanted the company to say to them today.

VIVUS dropped 13% despite seeing its losses narrow by 70% from year-ago levels, far exceeding the hopes of most investors. Yet another disappointing quarter of sales from the company's key Qsymia anti-obesity drug offset any enthusiasm from licensing deals for its erectile-dysfunction treatment. Moreover, the specter of potential new competition from Orexigen's (NASDAQ:OREX) Contrave later this year could pose an even bigger threat to VIVUS even if it can overcome its immediate need to drive sales higher.

Tenet declined 9% after reporting its own losses last night. Even after successfully completing its acquisition of Vanguard Health Systems, the hospital operator's guidance for 2014 disappointed investors, with EBITDA projections coming in 3% to 8% below what most investors had expected to see from Tenet. Even news yesterday that Tenet would expand a deal with Aetna (NYSE:AET) to accept insurance and participate in state-exchange plans in seven markets, further uncertainties about the way that health-care reform efforts will play out still exist. Many investors believe the risk-reward equation for Tenet doesn't look favorable enough to justify maintaining holdings in the stock.

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Dan Caplinger has no position in any stocks mentioned. The Motley Fool recommends and owns shares of SINA. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.

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