On the safety side, six patients treated across all three doses of VX-809 during the one-month monotherapy stage discontinued due to adverse events. Reasons for discontinuation included rash and "chest tightness," according to Boyle, who was surrounded by Wall Street investors after his presentation.

"We're going to pay attention to that," said Boyle from the middle of the Wall Street scrum, referring to the adverse events observed in the trial. Boyle added that one of his patients reported "mild to moderate" chest tightness but it didn't cause her to drop out of the study.

"I viewed it as a sign that something was going on, probably a sign of an effect," he said.

In a separate interview, I asked Boyle for his overall impressions of the VX-809/Kalydeco data:

"Overall, I'm encouraged and excited. When I first got the lung function averages, I said that's great but you can still hide a lot in averages. You can have one or two patients with an unexplainably large effect and not a lot of effect in most patients. But when I saw the waterfall plot and individual patient responses, and saw 55% of patients having what I consider a clinically significant improvement, that showed me that we have something here."

Dr. Steven Rowe of the University of Alabama, Birmingham and also an investigator in the VX-809/Kalydeco study, had a similar view:

"It's exciting to see the combination treatment come to fruition. It's a phase II design and we've been fooled before but this looks pretty convincing."

Rowe on what a 6% improvement in lung function means to a CF patient:

"FEV1 is a speedometer for CF patients. It's what they check every time they come to clinic and so, even small changes mean a fair amount to patients. These results compare favorably to many other drugs that have been approved and widely used for CF, so I think people would be excited about it."

--Written by Adam Feuerstein in Boston.

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Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.

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