Gilead Sciences (NASDAQ:GILD) is racking up billions of dollars in sales of its hepatitis C drugs every quarter, but competitors are angling for market share, and that has investors nervous that Gilead Sciences' revenue in the indication could slump. Drugs from Merck & Co (NYSE:MRK) and AbbVie (NYSE:ABBV) are commonly discussed as Gilead Sciences' biggest threat; but recently reported results from upstart Regulus Therapeutics (NASDAQ:RGLS) may mean it poses a far bigger risk to Gilead Sciences than they do.
