Image source: Westar Energy.

Stocks began the holiday-shortened week on Tuesday with a mixed performance. The Dow Jones Industrials finished the day down 86 points, losing close to half a percent on the day. But the tech-heavy Nasdaq gained ground, and the S&P 500's losses were much smaller than the Dow's. In the absence of any particularly noteworthy news over the weekend, investors largely looked forward to economic data later in the week. What has happened to the U.S. economy over the past month could play a large role in whether the Federal Reserve raises interest rates later this month, and that in turn could have an impact on the direction of the stock market. Even with the mixed performance, several stocks gained ground Tuesday, and among the best performers were Amarin (NASDAQ:AMRN), Marketo (NASDAQ:MKTO), and Westar Energy (NYSE:WR).

Amarin jumped 12% after the biopharmaceutical company released a statement saying its Vascepa omega3 product received a favorable ruling from the Food and Drug Administration. The FDA found that Vascepa capsules are eligible for market exclusivity for a five-year period as a new chemical entity, dating from the original FDA approval in July 2012. Although that means that exclusivity runs only until 2017, Amarin said that a 30-month statutory stay that patent litigation would trigger following the submission of an application for a generic version of the product, which would be allowed as of July 2016, will expire in early 2020. CEO John Thero believes that Vascepa might be protected as long as 2030 due to multiple patents covering the product.

Marketo jumped 9% after the maker of engagement marketing software and solutions agreed to an acquisition bid from private equity buyer Vista Equity Partners. The deal is worth $1.79 billion and values Marketo at $35.25 per share in cash. Even though that premium might sound small compared to Friday's closing price, the company said that the deal price is nearly two-thirds higher than where the stock traded on May 9, prior to initial reports that Marketo was in talks to sell itself to a potential buyer. Going forward, CEO Phil Fernandez believes that the acquisition will "enable us to successfully deliver on the bold vision we recently set forth: to give tomorrow's marketers and the C-suite an ultra-high-scale enterprise platform for customer engagement." Current Marketo shareholders might not see any further upside, but the company is optimistic about its continuing evolution with Vista.

Finally, Westar Energy rose 6%. The utility company agreed to an acquisition from peer Great Plains Energy with a total value of $12.2 billion including assumed debt. The combined Westar and Great Plains will have more than 1.5 million customers in Kansas and Missouri, uniting two neighboring companies with a total of about 13 gigawatts of electrical generation capacity, 10,000 miles of transmission lines, and more than 50,000 miles of distribution lines. The deal will pay Westar shareholders $51 per share in cash plus about $9 per share in common stock of Great Plains, subject to adjustment if the price of Great Plains stock moves more than 7.5% in either direction between now and the closing date. The relatively small premium raised some eyebrows, but the move should produce useful synergies that are likely to reward Great Plains shareholders in the long run.