Shares of Proteostasis Therapeutics Inc. plunged 58% on heavy volume in morning trade Monday, enough to pace all decliners trading on major U.S. exchanges, after biopharmaceutical company announced results from a phase 1 study of its cystic fibrosis (CF) treatment. Trading volume ballooned to 7.6 million shares, compared with the full-day average of 1.2 million shares. The company said the increase in ppFEV1 at day 14 of a statistically significant 5 percentage points versus baseline was observed in the 600 milligram PTI-801 cohort. Analyst Geoffrey Porges at SVB Leerink said the results CF did not meet the efficacy of Vertex Pharmaceuticals Inc.'s medicines, as that 5% was below the 13%-14% hurdle established by Vertex. Porges believes the results of Proteostasis' trial removes the final "long-shot competitor" to Vertex's CF portfolio. Vertex shares gained 1.0% in morning trade. Proteostasis's stock has lost 66.3% over the past 12 months, while Vertex shares have rallied 13.8% and the S&P 500 has gained 7.8%.