Seres Therapeutics Stock Tanks 78% After 'unexpected' Negative Midstage Trial Results

Seres Therapeutics Inc. shares cratered 78% in pre-market trade Friday after the company said interim phase 2 trial results for its colon infection treatment weren't statistically significant. The company's chief executive officer, Roger Pomerantz, called the results "unexpected" in light of a previous phase 1b trial and other supporting data. The treatment, SER-109, is intended for multiply recurrent Clostridium difficile infection, which is commonly spread in hospitals and other health care institutions. Shares of Seres rose 21.2% over the last three months, compared with a 5.1% rise in the S&P 500 .