Gossamer Bio Inc. shares (NASDAQ:GOSS) fell 74.6% to $2.36 Dec. 6 after the disclosure of phase II results that, while meeting the study's primary endpoint of reducing pulmonary vascular resistance vs. placebo, failed to show the company's pulmonary arterial hypertension (PAH) candidate, seralutinib, holding its own against the performance of Merck & Co. Inc.'s PAH candidate, sotatercept, in separate PAH studies.