CAMBRIDGE, Mass. (TheStreet) –Vertex Pharmaceuticals(VRTX) released clinical trial results Wednesday demonstrating that an experimental drug VX-770 significantly improved lung function by more than 10% and provided other clinical benefits in adults with a specific form of cystic fibrosis. the results from the phase III study represent a potential scientific breakthrough because VX-770, if eventually approved, would be the first and only drug to repair the underlying genetic cause of cystic fibrosis rather than merely treating the symptoms of the disease. Vertex shares were up 20% to $45.90 in Wednesday pre-market trading. VX-770 corrects a genetic mutation found only in approximately 4% to 7% of the 70,000 cystic fibrosis patients worldwide. the number of cystic fibrosis patients who stand to benefit from VX-770 may be small, but the results from the study are so strong and clinically meaningful that Vertex stands to generate peak annual sales from VX-770 in the range of $400 million to $600 million if the drug is priced comparable to other expensive treatments for rare, genetic disorders. Vertex said Wednesday that it plans to seek regulatory approval for VX-770 in the second half of the year. Results from the phase III study known as STRIVE reported by Vertex showed that treatment with VX-770 through 24 weeks resulted in a mean absolute improvement in lung function of 10.6% compared to placebo. This clinical benefit in favor of VX-770 — the primary endpoint of the STRIVE study — was highly statistically significant and was even sustained through 48 weeks of treatment. the STRIVE study enrolled 161 patients aged 12 and older. to put the 10.6% absolute improvement in lung function in perspective, Vertex designed the phase III study with the intent that a 4.5% improvement would be enough to yield positive results. Wall Street’s professional biotech investors, as a group, were expecting positive results from the VX-770 study but just barely. In a survey of investors conducted by ISI Group biotech analyst mark Schoenebaum released Tuesday, 87% of respondents believed VX-770 would improve lung function by 5% or less over placebo. just 6% of the investors in Schoenebaum’s poll believed VX-770 could improve lung function by 10% or more.