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

What: Less than a week after presenting at a biotech industry conference, and days after a major hedge fund reported that it doubled its ownership stake in the company, shares in Horizon Pharma (NASDAQ:HZNP) are jumping by nearly 10% today, only a week before it's scheduled to announce fourth-quarter earnings results.

So what: Since acquiring the specialty arthritis NSAID drug Vimovo from AstraZeneca (NYSE:AZN) at the end of 2013, Horizon Pharma has been on a bit of a roll. Thanks to $43.2 million in sales for Vimovo, Horizon's sales surged 211% year over year to $75.1 million during the third quarter.

Source: Horizon Pharma Vimovo Sales

Vimovo's sales of nearly $120 million through the first nine quarters of 2014 dwarfs the drug's full-year sales of $20 million in 2013, when it was still marketed by AstraZeneca. That surge in sales indicates that AstraZeneca's $35 million price tag for Vimovo has proven to be a bargain for Horizon. Especially since Vimovo's sales success has led to Horizon outpacing analysts' EPS predictions in each of the past two quarters, including a 41% beat when the company reported adjusted EPS of $0.24 in Q3.

Horizon's success with Vimovo hasn't gone unnoticed by investors, who have been reducing their short positions and increasing their long exposure to the company. In January, the number of shares held short in Horizon dropped from 14.02 million to 12.22 million, and this past week, regarded hedge fund manager Kingdon Capital announced that it had increased its long position in the company by about 90% to more than 6 million shares during the fourth quarter.

Now what: Investors' recent decisions on Horizon Pharma seem to suggest they think the company's fourth-quarter results will be solid when they're reported on February 27th. Analysts expect the company will report fourth-quarter sales of $95.54 million and full-year sales of $288.2 million for 2014. Wall Street is also estimating that Horizon's EPS will total $0.22 for Q4 and $0.80 for the full year.

If Horizon Pharma reports that momentum for Vimovo isn't waning, and if the company can use Vimovo's sales growth to boost demand for its other drugs, Horizon's profit-friendly winning streak may continue.