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Vertex tumbles 18% on CF drug update

BOSTON (MarketWatch) -- Shares of Vertex Pharmaceuticals tumbled 18% to $53.31 Tuesday on news that it has revised preliminary results from a Phase II study for its cystic fibrosis drugs VX-809 and Kalydeco. The revised results show that the drug combination was less powerful in treating the genetic disease than previously reported. On May 7, Vertex shares soared almost 50% on news that the combination appeared to be unusually effective in treating the life-threatening lung disease. Vertex said that full study results should be available mid-year.