Shares in pharmaceutical firm AstraZeneca (LON:AZN) fell over 15 percent in early trading on Thursday, after disappointing results from a key drug trial.

Shares in the company plunged after it reported that the development of new lung cancer drug Mystic had failed to show the positive results expected, with the trial not reaching its “endpoints” for progression free survival.

The Mystic drug was one of AstraZeneca’s most prominent drugs in development, but initial results from the study found that the combination of two injectable drugs, durvalumab and tremelimumab, was no more effective at stopping disease progression in affected patients than chemotherapy.

The Mystic drug was one of AstraZeneca’s most prominent drugs in development, with Jeffrey Holford, an analyst at Jefferies, telling the Financial Times that the setback in the Mystic trial was “a significant blow”. He said his firm estimated this would remove “[about] 10 per cent to 15 per cent of mid term earnings and valuation” from AstraZeneca.

Total revenue at the company fell 11 percent to $10,456 million, but operating profit rose 37 percent to $1,842 million. Reported earnings per share were also up 58 percent to $0.80.

The company saw 3 percent growth in emerging markets in the first half of the year, underpinned by China sales growth of 3 percent. However, it warned that economic conditions in Latin America and Saudi Arabia limited overall growth in the region.