There are very few sure things in biotech. Investing in the sector involves making a lot of educated guesses and weighing the rewards for being right against the consequences for being wrong.

One company that has a drug I feel pretty good about is Encysive Pharmaceuticals (NASDAQ:ENCY). Encysive recently released phase 3 clinical trial data on its drug Thelin for treating pulmonary arterial hypertension (PAH), or high blood pressure in the lungs. PAH is a big problem because the heart has to work harder than normal to move blood through the lungs. This causes fatigue, chest pain, and eventually heart failure. PAH is chronic and incurable without a heart and lung transplant.

Drugs for PAH can improve the patient's capacity for physical activity and also increase the length of time before symptoms worsen. One approved drug is Tracleer, from Swiss company Actelion. Tracleer has been commercially successful, with sales of several hundred million dollars a year.

While Actelion's Tracleer is the first mover, Encysive's Thelin is poised to capture a big chunk of this market. The recently released clinical trial data showed that Thelin works just as well as Tracleer and appears to be safer. Thelin also needs to be taken only once a day instead of twice, like Tracleer.

Encysive is going to file a new drug application with the Food and Drug Administration in May and seek a priority review. If it gets a priority review, Thelin could be on the market by the end of the year. If there's a standard review, the drug could launch during the first half of next year. Given that Thelin, at the very least, looks to compare favorably to Tracleer, I expect that the drug will reach several hundred million dollars in sales. Seeing as Encysive has a current market cap of $670 million, this is a situation that looks pretty good to me.

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Fool contributor Charly Travers is the biotech analyst for Motley Fool Rule Breakers. He does not own shares of any company mentioned in this article. The Motley Fool has a disclosure policy.