In the absence of any major economic data, the stock market continued to gain ground today, with the S&P 500 Index (SNPINDEX:^GSPC) even ending at an all-time high. Three stocks, however, finished as standout laggards: Gilead Sciences (NASDAQ:GILD), Wynn Resorts (NASDAQ:WYNN), and Boston Scientific Corporation (NYSE:BSX) were each firmly in the red Monday. The S&P 500, for its part, tacked on 1 point, or less than 0.1%, to end at 1,951.

Shares of Gilead Sciences, whose flagship product, Sovaldi, treats hepatitis C, shed 4.1% today, as a new, deep-pocketed competitor threw its hat in the ring. Perhaps you've heard of Merck? Well, the $170 billion pharma giant was so impatient to jump-start a comprehensive hepatitis C treatment that it paid the highest ever premium in a health-care deal, according to Bloomberg, to acquire Idenix Pharmaceuticals today. The $3.85 billion acquisition rewarded Idenix investors to the tune of 229% today. Gilead Sciences, on the other hand, is now pressured to either lower the price of its $84,000 treatment or invest more heavily in Sovaldi to differentiate it from Merck's new combo offering.

Casino operators Wynn Resorts also had a rough day on Wall Street today, losing 2.9% by the ring of the closing bell. Wynn investors should count themselves lucky for the simple reason that the gaming company has firmly established itself in Macau, the 21st century's gambling capital of the world. But participating in China's exclusive and emerging gambling hotspot brings its own risks, and right now the biggest risk for investors is the possibility that the explosive growth in the region is slowing. After a decelerating month of revenue growth in May, Wells Fargo reported that Macau gaming revenue, by its estimates, continues to decelerate in early June.

An interventional coronary stent. Source: Boston Scientific

Lastly, shares of Boston Scientific fell 2.8% Monday, kicking off the week on a bearish note. While revenue at Boston Scientific has been trending steadily lower for years -- a phenomenon no investor wants to see -- there's no real, compelling reason behind today's slump. The health care sector happened to be the second-worst performer in the stock market today, so Boston Scientific was already fighting an uphill battle Monday, but its long-term prospects aren't quite as dire. The company acquired Bayer's interventional division for $415 million last month, which should create operational synergies and complement its own interventional division ("interventional" products treat blood flow issues).

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