An experimental AstraZeneca drug that failed last year as a treatment for a rare cancer of the eye has been awarded special "orphan" status in the United States for a type of thyroid cancer.

The British drugmaker, which is relying on cancer treatments to revive its fortunes following a wave of patent expiries, said on Thursday the decision showed the potential importance of selumetinib for some patients.

Orphan status is awarded to medicines promising significant benefit in treating rare, life-threatening diseases and the designation provides companies with special development and market exclusivity incentives.

AstraZeneca's drug is being tested for patients with advanced differentiated thyroid cancer who fail to respond adequately to radioactive iodine.

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Selumetinib, which belongs to a class of cancer drugs known as MEK inhibitors, failed to meet its goal in a late-stage trial for uveal melanoma in July 2015.

The drug is also being investigated as a treatment for advanced non-small cell lung cancer. However, it is viewed by analysts as less important commercially than AstraZeneca's recently launched cancer drugs Tagrisso and Lynparza, and its experimental product durvalumab.