The big winners from last week's American Association for the Study of Liver Diseases meeting were Gilead Sciences Inc. (NASDAQ:GILD) and Idenix Pharmaceuticals Inc. (NASDAQ:IDIX), which gained 14% and 12%, respectively, on Monday after positive HCV data.

Gilead's stock rose $8.92 - which translates to $6.8 billion in market cap - to close Monday at $73.93, valuing the company at $56 billion.