Shares of Syndax Pharmaceuticals Inc. (NASDAQ:SNDX) fell 17.1 percent to $5.01 Friday on news that adding its HDAC inhibitor, entinostat, to an aromatase inhibitor failed to deliver a statistically significant improvement in the length of time women with hormone receptor-positive, HER2-negative breast cancer lived without worsening of their cancers. The outcome, from the ongoing phase III study E2112, dashed hopes of an early regulatory filing, putting the focus on the trial's other co-primary endpoint, overall survival (OS).