The Boston-based drug maker’s stock soared a stunning 21% in Wednesday trading after its triple drug combination therapy for cystic fibrosis (CF)—a rare genetic disorder that eats away at the lungs, pancreas, and other organs—posted promising results in early clinical trials.

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Wall Street investors were hoping that Vertex’s cocktail could improve certain metrics of lung function by at least 2.5 percentage points, according to CNBC. The company says that it did that and more—to the tune of a 9.6 percentage point (or more) improvement.

That’s critical for a company with a rare disease focus. There are about 30,000 cystic fibrosis patients in any given year, but few actually have treatment choices. A regulatory win for Vertex’s combination therapy could prove critical.

The company’s financial success is also inextricably linked with pricing, as is the case with many “orphan drug” companies that make treatments for rare conditions. Vertex has had to wrangle with regulators in other countries over whether or not its CF drugs are worth the price. But promising results in such a hard-to-reach treatment space may be enough to guarantee regulatory success, especially if future trial results prove promising.