U.S. HOT STOCK FUTURES: HOT STOCKS TO WATCH

Among the companies with shares expected to actively trade in Tuesday's session are Zynga Inc. (ZNGA), Achillion Pharmaceuticals Inc. (ACHN) and A. Schulman Inc. (SHLM).

Zynga's founder Mark Pincus announced Monday that he was stepping down as CEO of the troubled game maker and will be replaced by Don Mattrick, who has been leading Microsoft Corp.'s (MSFT) Xbox division. Shares rose 5.5% to $3.24 after hours.

Achillion said the U.S. Food and Drug Administration has put a clinical hold on sovaprevir, its experimental oral hepatitis C treatment, due to safety concerns. Shares dropped 22% after hours to $6.50.

A. Schulman's fiscal third-quarter earnings fell 69% amid continued sluggishness in European markets and higher-than-expected costs in Latin America, where the company has been consolidating its Brazilian operations. The company also lowered its full-year per-share earnings estimate. Shares fell 13% after hours to $24.10.

Alliance Fiber Optic Products Inc. (AFOP) expects second-quarter sales to exceed its already increased outlook as demand remained strong through the quarter. Shares were up 11% at $24.31 in after-hours trading.

Kidney dialysis centers owned by DaVita Healthcare Partners Inc. (DVA) and Fresenius Medical Care AG (FMS) could receive 9.4% less in Medicare payments, starting in 2014, based on new rates proposed by the federal government. News of the possible rate cuts, which came late Monday, sent shares of DaVita falling 7.6% to $111.96 in after-hours trading. While lower rates were expected from the Centers for Medicare and Medicaid Services, the proposed reductions were deeper than some expected.

Information and measurement company Nielsen Holdings NV (NLSN) will join the S&P 500 index, replacing Sprint Nextel Corp. (S) following the wireless carrier's takeover by Japan's SoftBank Corp. (9984.TO), said S&P Dow Jones Indices. Nielsen's shares rose 3.7% to $34.50 after hours.

Xyratex Ltd.'s (XRTX) fiscal first-quarter profit fell 58% as the data-storage firm continued to suffer from revenue declines in both of its major business units. But shares rose 6.6% to $10.90 in after-hours trading as the earnings results beat the company's own projections.

 
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Government services provider Maximus Inc. (MMS) forecast fiscal 2014 revenue above analyst expectations and said it has added more than $125 million in new contracts related to the health-insurance exchange market under the Affordable Care Act.

Internet security software and technology company VirnetX Holding Corp. (VHC) said Apple Inc. (AAPL) has filed to appeal a $368 million award the Internet security firm was granted by a jury in February in a patent infringement case.

Walt Disney Co. (DIS) Chairman and Chief Executive Robert Iger will remain CEO until 2016, one year later than previously planned, pushing back a resolution to the long-standing question of who will succeed him atop the family-entertainment giant.

-Write to Nathalie Tadena at [e-mail]

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