AstraZeneca cleared to resume enrolment in cancer drug trials

* Head and neck cancer studies resume patient recruitment

* Trials involve AstraZeneca (NYSE: AZN - news) 's immunotherapy durvalumab (Adds shares, further details on immunotherapy)

By Ben Hirschler

LONDON, Nov 22 (Reuters) - U.S. officials have given a green light for two clinical trials testing AstraZeneca's immunotherapy drug durvalumab in head and neck cancer to resume recruiting patients, lifting a hold imposed following cases of bleeding.

One of the late-stage Phase III trials had already re-opened for new patient enrolment and the second was expected to resume recruitment shortly, the British drugmaker said on Tuesday

News of the partial hold on the trials, imposed at the end of last month, had spooked investors since durvalumab is AstraZeneca's most important pipeline medicine.

Shares (Berlin: DI6.BE - news) in AstraZeneca gained around 1 percent on Tuesday as the company announced the lifting of the partial clinical trial hold by the U.S. Food and Drug Administration.

Durvalumab is being tested on its own and with another immune system-boosting drug called tremelimumab in various cancers, including lung cancer, which represents the biggest market.

Although trials of the drug in these other tumour types were not affected by the head and neck issue, there had been concerns there might be a problem with durvalumab or tremelimumab that could disrupt wider development.

Data due in lung cancer in the first half of 2017 will be critical in determining AstraZeneca's position in the cancer arena, where it faces immunotherapy rivals including Merck (Jakarta: 28586808.JK - news) , Bristol-Myers Squibb and Roche.

Bleeding is a known complication in treating head and neck cancer, given the proximity of tumours to major blood vessels and use of prior cancer therapies, which may involve surgery and radiation.

AstraZeneca had initially hoped that it might win early approval of durvalumab in head and neck cancer but it said on Nov. 10 it had given up the idea due to changes in the competitive landscape.

This follows the approval of Merck (LSE: 0O14.L - news) 's similar drug Keytruda for the condition, which reduced the case for special regulatory treatment of durvalumab. (Reporting by Ben Hirschler; Editing by Mark Potter/Keith Weir)