* Selexipag reduces risk of morbidity/mortality by 39 pct
* Jefferies analysts forecast peak sales of $800 mln
* Shares rise almost 15 pct in early trade (Adds shares, analyst)
ZURICH, June 16 (Reuters) - Actelion Ltd said its experimental heart and lung drug Selexipag met its primary goal in a late-stage study, giving the Swiss biotech company a potential second big seller to replenish its product pipeline.
Selexipag is the third drug from Actelion to treat pulmonary arterial hypertension (PAH), a progressively worsening condition characterised by abnormally high blood pressure in the arteries of the lungs. The cause is unknown and the disease has no cure.
The positive result is a boost to Europe's biggest biotech company and should reassure investors that the firm's long-term growth prospects are on course, after another PAH treatment, Opsumit, won approval in Europe and the United States.
Both drugs are successors to Actelion's mainstay product Tracleer, which makes up over 80 percent of sales, and loses patent protection in 2015.
Shares in Actelion, which have already gained more than 20 percent so far this year in anticipation of the data, jumped 14.9 percent to 104.5 Swiss francs in early trade.
Deutsche Bank analyst Richard Parkes said the results look like a "close-to-best case outcome."
"This should allow it to fully offset the Tracleer patent cliff over 2015-17 and adds significant confidence over the longevity of Actelion's core PAH franchise that was arguably previously still lacking," Parkes wrote in a note.
Jefferies analysts described the results as "impressive" and said their original peak sales estimate of $800 million would now likely be conservative.
Results of the Phase III study involving 1,156 patients found the drug reduced the risk of a morbidity/mortality event by 39 percent versus a placebo in patients suffering from PAH.
Chief Executive Jean-Paul Clozel said in a statement he was "overwhelmed" by the results, adding Actelion planned to submit Selexipag for approval with health authorities as soon as possible once analyses of the study have been completed.
Selexipag, which was originally discovered by Japan's Nippon Shinyaku, is an oral drug and thus more convenient than some other treatments that target the prostacyclin pathway that must be inhaled or administered intravenously.
Actelion said detailed results of the study will be presented at upcoming congresses and in peer review publications. (Editing by Sophie Walker)