They analyzed each closing stock price before and after the date of a public announcement and found that the average stock price 120 days before a phase III clinical trial announcement showed an increase of 13.7 percent for companies that reported positive trials and a 0.7 percent drop for those reporting negative trial results ( here is the abstract).

FORBES: Why Pharma Stocks May Rise Before Trial Data Is Released

Of the 55 deals mergermarket covered for public bidders over the past six months, 24 had a share price increase after the deal announcement.

FORBES: Recent M&A Positive For Acquirers' Share Prices