May 16 (Reuters) - The U.S. Food and Drug Administration

on Thursday granted accelerated approval to Amgen's ( AMGN )

tarlatamab, a targeted immunotherapy for treating adults with

advanced small cell lung cancer that has worsened despite

chemotherapy.

The therapy, marketed under the name Imdelltra, is part of

Amgen's ( AMGN ) pipeline of bispecific antibodies, which are designed to

attach to a cancer cell and an immune cell, bringing them

together so that the body's immune system can kill the cancer.

Results from a mid-stage trial published last year in the

New England Journal of Medicine showed that tumors shrank in 40%

of patients receiving 10 mg of tarlatamab by intravenous

infusion every two weeks.

More than half of the patients whose tumors responded to

tarlatamab did not see their disease worsen for at least six

months.

The most common side effect was cytokine release

syndrome, a potentially dangerous condition that occurs when the

body's immune system responds over aggressively to infection or

immunotherapy drugs.

Most lung cancer cases are non-small cell, while up to 15%,

according to the American Cancer Society, are the more

aggressive small cell variety targeted by Amgen's ( AMGN ) drug,

tarlatamab.

The disease, which is diagnosed in about 35,000 U.S.

patients annually, is "one of most rapidly proliferating and

most aggressive cancers there is," Jay Bradner, Amgen's ( AMGN ) chief

scientific officer, said in an interview ahead of the decision.

Bradner explained that the arm of tarlatamab that

targets small cell lung cancer cells attaches to a protein

called DLL3.

Amgen ( AMGN ) said it will need to complete its larger, pivotal

trial in advanced small cell lung cancer to receive full FDA

approval of the drug.

The company is also testing tarlatamab for treating

patients with earlier stage small cell lung cancer.

If those studies prove successful, Wall Street analysts

have said tarlatamab could represent an over $2 billion annual

sales opportunity for the company.