Seres Thera tanks as SER-287 Phase IIb misses goal

Shares in USA-based microbiome therapeutics platform company Seres Therapeutics (Nasdaq: MCRB) slumped 58% to $8.86 in heaving trading, which reached 10.1 million shares by late Thursday afternoon compared with the stock's daily average of about 827,000, according to data compiled by Yahoo Finance.

The fall came after Seres announced top-line results from the Phase IIb ECO-RESET study evaluating SER-287 in patients with mild-to-moderate ulcerative colitis (UC). The study did not meet its primary endpoint of improving clinical remission rates compared to placebo. Both dosing regimens of SER-287 were generally well tolerated. Given the lack of a clinical efficacy signal identified in ECO-RESET, the company has decided to close the open label and maintenance portions of the study.