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.

Good morning, fellow Foolish investors! It's time to check in on the top stories in the health care sector this morning.

Sarissa reportedly pushing for board seats at Ariad?
As has become custom of late, Ariad Pharmaceuticals (NASDAQ: ARIA) is moving upwards in premarket trading based on rumors. Specifically, the company's shares are up 7.45% with over 1.4 million shares exchanging hands in extended hours trading, at the time of writing this article.

Today's action is apparently linked to a Reuter's blog stating that Sarissa Capital Management is seeking seats on Ariad's board prior to the upcoming election on Feb. 20, much in the same way they did after taking a big stake in VIVUS Corporation last year. If you recall, Sarissa Capital and First Manhattan shook up VIVUS's board in 2013 in an attempt to right the ship so to speak. 

If this report turns out to be true, however, I don't view it necessarily as a good thing. Sarissa's involvement in VIVUS has not changed the fortunes of the company in the least, and instead, has led to instability within the executive management. In my experience, activist investors tend to cause more harm than good, and it's important to keep in mind that Ariad doesn't have a managerial problem; it has a drug with safety issues problem. Then again, this could turn out to be yet another baseless rumor swirling around Ariad. So, stay tuned!

Cigna's earnings disappoint
Continuing the parade of earnings in the health care sector, Cigna Corporation (CI) reported this morning, missing earnings per share estimates by $0.10, but beating on revenues by a hefty $850 million. Investors shouldn't be too down on the company this morning, however, because the earnings release was generally positive. Annual revenues increased by 11% to $32.4 billion, and Cigna increased earnings per share for the year by a stately 13%.

Turning to the miss, Cigna's earnings missed estimates largely because of a $40 million special charge after taxes due to a restructuring program instituted by the company. Given that this is not expected to be a reoccurring event and instead a one time charge, I think investors would be wise to focus on the broader picture that is emerging, namely strong annual growth that will continue into 2014. The reorganization should also help falling operating margins, which hurt the company's fourth quarter performance. In sum, you might want to dig deeper into this diversified health care company. 

Shire is bummed over late-stage clinical trial results
Shares of Irish biopharma Shire (NASDAQ: SHPG) are down only slightly in premarket trading this morning after the company's experimental drug Vyvanse for major depressive disorder, or MDD, failed to meet its primary endpoints in two late-stage studies. Specifically, the studies showed that while Vyvanse is generally safe, it does not perform better than placebo at reducing symptoms associated with MDD. Because the effectiveness of Vyvanse and placebo were relatively similar at treating MDD, Shire has decided to discontinue the drug's clinical development for this indication altogether. Vyvanse is approved in the U.S. as a treatment for ADHD; so, these two studies were aimed at expanding the drug's current label. 

Although negative clinical trial results are always disappointing, they are an integral part of investing in this sector. On the bright side, large biopharmas like Shire do offer investors strong commercial portfolios that help to soften the blow when these inevitable events occur. Put simply, I don't expect Vyvanse's recent clinical failure to be a major issue going forward.