(Reuters) - Infinity Pharmaceuticals stopped two mid-stage trials of its experimental drug to treat a rare bone marrow disorder and a type of bone cancer, sending the company's shares down 21 percent in premarket trade.

The company decided to stop the bone cancer trial after an independent data monitoring committee said the drug, saridegib, would not perform better than a placebo in increasing survival in patients without the cancer worsening.

Infinity also pulled the plug on a trial to treat myelofibrosis, a rare bone marrow disorder, after initial data did not satisfy its criteria for expanding the trial.

In January, Infinity had stopped another trial on saridegib as a treatment for pancreatic cancer.

Shares in Infinity Pharmaceuticals closed at $13.88 on Friday on the Nasdaq.

(Reporting by Balaji Sridharan in Bangalore; Editing by Roshni Menon)