UPDATE 1-Celgene to stop testing Crohn's drug, shares drop

(Adds details on the trials, drug's sales forecast, share movement)

Oct 19 (Reuters) - Celgene Corp said it would abandon testing a drug to treat Crohn's disease, an inflammatory bowel disease, following a risk-benefit analysis by a data monitoring committee, in a major setback to the drugmaker's pipeline.

The U.S. biotechnology company's shares fell 9.6 percent to $126.37 in extended trading on Thursday.

The company said it would end two studies of the drug, mongersen, and would not initiate a third. The drug was being tested in late-stage and extension studies as a treatment for Crohn's.

Mongersen has been forecast to rake in sales of more than $1 billion by 2023, according to Thomson Reuters I/B/E/S.

The interim futility analysis by the data committee found no meaningful safety imbalances, Celgene said.

The company is waiting to review full data from a mid-stage study testing mongersen as an ulcerative colitis treatment to determine next steps.

Celgene is also testing ozanimod as a treatment for inflammatory bowel disease.

Inflammatory bowel diseases, which include Crohn's, affect about 1.6 million Americans, according to Crohn's & Colitis Foundation.

Crohn's affects the lining of the digestive tract and can cause abdominal pain, diarrhoea and rectal bleeding. (Reporting by Tamara Mathias in Bengaluru; Editing by Sriraj Kalluvila)