Vertex Pharmaceuticals Inc (VRTX.O) said on Thursday its combination cystic fibrosis treatment improved patient lung function in a mid-stage clinical study, but its shares fell as much as 12 percent amid investor skepticism the results are not as strong as they look.
Vertex presented final results from a Phase II study of its drug Kalydeco in combination with an experimental drug, VX-809. Interim results from the trial presented earlier this year sent the company's shares soaring.
Some of the gains were later lost after the company was forced to revise the data due to a statistical mistake in which it confused relative with absolute results. The final results presented on Thursday also contained ambiguities that unsettled investors.
In particular, the company did not present exactly comparable results between the interim and final data.
"This non apples-to-apples disclosure has created investor doubt that the data are 'real,'" said Mark Schoenebaum, an analyst at ISI Group, in a research note.
Company executives told analysts on a conference call that even though it did not present exactly comparable results, the final results should stand alone and indicate the treatment is effective at the highest dose and warrant moving forward into late-stage clinical development.
Kalydeco, which in January became the first drug approved to treat the underlying cause rather than symptoms of the lung disease, helps about 4 percent of cystic fibrosis patients with a specific gene mutation.
Vertex is hoping that the drug, when combined with VX-809, will eventually be able to treat the larger cystic fibrosis population.
Cystic fibrosis causes the thin layer of mucus that helps keep lungs free of germs to thicken, clogging airways and damaging the lungs. The average life expectancy for the disease is 37 years as damage to the lungs progresses limiting the ability to breath.
Vertex shares tumbled 8.3 percent to $56.05 in morning trading on Nasdaq and fell as low as $53.83.
(Reporting By Toni Clarke, Lewis Krauskopf and Bill Berkrot; editing by Jeffrey Benkoe)