The U.S. Food and Drug Administration (FDA) has granted Breakthrough Therapy Designation for Imfinzi, an experimental drug developed by AstraZeneca and MedImmune.

The drug is used for the treatment of patients with "locally-advanced, unresectable non-small cell lung cancer (NSCLC) whose disease has not progressed following platinum-based chemoradiation therapy," according to AstraZeneca.

"For patients who have not progressed following chemoradiation therapy the only current option is active monitoring. Unfortunately, for the majority of patients, their cancer will progress to metastatic disease, typically within 12 months. Imfinzi is the first immuno-oncology medicine to show a clinically-significant benefit in this earlier, non-metastatic setting, so following the Breakthrough Designation we hope to bring it to patients as soon as possible," said Sean Bohen, executive vice president, global medicines development and chief medical Officer at AstraZeneca.

The approval follows a 17 percent drop in AstraZeneca shares after early testing of the drug proved disappointing compared to a Merck product.

The designation helps expedite the development and regulatory review of new medicines for serious conditions.

This is the fourth such designation given to AstraZeneca for a New Oncology cancer medicine over the last three years. Delaware is the North American headquarters of the pharmaceutical company.