May 1 (Reuters) - Vertex Pharmaceuticals Inc VRTX.O on Thursday said a combination of its cystic fibrosis drug Kalydeco with an experimental compound was shown to improve lung function in a mid-stage trial, and its shares rose 10 percent after the news.

The study found that treatment with both drugs for 28 days resulted in a 4.6 percentage point improvement in mean lung function for patients with two specific genetic mutations.

"It is good data and some believe it does have an incremental positive read-through to the all-important Phase 3 data later this summer," said RBC Capital Markets analyst Michael Yee.

The most common side effects seen during the trial included cough, headache and upper respiratory tract infection.

Shares of Vertex, which closed at $68.95 in regular Nasdaq trading, were up $7.04 at $75.99 after hours.

(Reporting By Deena Beasley; Editing by David Gregorio)

((deena.beasley@thomsonreuters.com)(213 955 6746)(Reuters Messaging: deena.beasley.thomsonreuters.com@reuters.net))

Keywords: VERTEX/