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.

The stock market had a quiet day, with the Dow Jones Industrials and other major market benchmarks clinging close to the unchanged level. Yet even though a combination of mixed economic data and tepid earnings from several key companies kept the market from making much more headway from its record-high levels, J.C. Penney (NYSE:JCP), Dendreon (NASDAQ:DNDN), and Petroleo Brasileiro (NYSE:PBR) all posted sizable gains on the day. Let's take a closer look to find out what sent those stocks soaring today.

J.C. Penney climbed almost 9% as CEO Myron Ullman repeated earlier calls that he sees the beleaguered retailer's sales starting to improve. The company still expects to report positive same-store sales when it gives its fiscal third-quarter results next month, but investors might do well to consider whether Ullman is protesting too much with his repeated assertions about J.C. Penney's success. Still, with talk of potential bankruptcy swirling around the company, J.C. Penney has a lot farther to go before investors should feel confident about any turnaround.

Dendreon picked up 11% amid reports that the company might put itself up for sale. The stock has seen immense volatility during its storied history, with its Provenge treatment for prostate cancer having raised hopes for huge sales that simply never panned out to the extent bullish shareholders had expected. Even with the gains, Dendreon stock has fallen by almost half just since August, and it's uncertain how much a buyer would be willing to pay for a lead drug that has fallen short of expectations and a pipeline whose value would be hard to define.

Petrobras gained 9%, as the Brazilian oil giant considered what could be massive changes to the way it sets prices for the gasoline and diesel fuel it sells. The state-run company has posted substantial losses on fuel sales, but with demand outpacing supply, Petrobras actually has to import diesel and gasoline at higher international prices only to sell them at a loss. Changing that strategy could lead to bigger profits for Petrobras, although civil unrest could result if higher fuel costs lead to more inflationary pressures for the emerging-market nation.

Fool contributor Dan Caplinger has no position in any stocks mentioned. You can follow him on Twitter: @DanCaplinger. The Motley Fool recommends Petrobras. 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.