Pharmaceutical companies have had some of the best-performing stocks over the last couple of years thanks to an innovation boom that has produced a host of new game-changing drugs, from Gilead Sciences ' revolutionary new cancer treatment Keytruda. Pharma stocks have crushed the broader market in recent years, as shown by the incredible performance of the iShares Nasdaq Biotech Index to favor its newly approved hepatitis C therapy Viekira Pak for genotype 1 patients, over Gilead's competing drugs, appears to mark a sea change in the pharma landscape that could trigger a major reversal in these stocks.