Myelofibrosis is a chronic disorder which occurs when the scar tissue formation forces the production of blood cells to move from the bone marrow to the spleen and liver, resulting in organ enlargement.

Celgene has been approved by Food and Drug Administration (FDA) for the treatment of myelofibrosis as Bristol-Myers Squibb Co has agreed to buy Celgene for cash and stock in the largest pharmaceutical industry merger ever. Celgenes Inrebic, a Janus kinase (JAK) inhibitor, acts by inhibiting inflammation-causing Janus kinases enzymes.

Another JAK inhibitor, Incyte Corps Jakafi, was approved in the United States in 2011 to treat certain bone marrow and blood disorders.

Inrebic was approved by US FDA based on positive outcome from a trial of 289 patients with myelofibrosis where the drug was evaluated against a placebo.

The treatment comes with a boxed warning, the drug regulators harshest, flagging concerns that involve serious and fatal brain damage.