PrivateBancorp Inc. (Nasdaq:PVTB), GMX Resources Inc. (Nasdaq:GMXR) and Century Aluminum Co. (Nasdaq:CENX) are among the most actively traded companies in Thursday's trading among companies with market capitalizations under $1 billion.

Also included among the results: Medarex Inc. (Nasdaq:MEDX), Vanda Pharmaceuticals Inc. (Nasdaq:VNDA), CommVault Systems Inc. (Nasdaq:CVLT), Medicines Co. (Nasdaq:MDCO), STEC Inc. (Nasdaq:STEC) and Apollo Investment Corp. (Nasdaq:AINV).

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