> ## Content Index
> Fetch the complete content index at: https://www.fdaweb.com/llms.txt
> Use this file to discover other available public pages before exploring further.

# Orphan Status for Experimental Myelofibrosis Therapy
- URL: https://www.fdaweb.com/orphan-status-for-experimental-myelofibrosis-therapy/
- Published: 2026-01-22T12:00:00.000Z
- Updated: 2026-09-14T15:31:16.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5160531

FDA has granted Opna Bio an orphan drug designation for its investigational treatment OPN-2853 (zavabresib), a small-molecule bromodomain and extra-terminal motif inhibitor, for myelofibrosis, which is characterized by progressive scarring of the bone marrow and leading to impaired blood cell production and symptoms that can include severe fatigue, anemia, and enlargement of the spleen.

Zavabresib is currently being evaluated in an investigator-sponsored Phase 1 study known as PROMise, which is being conducted at the University of Oxford in collaboration with Cancer Research UK. The study focuses on patients whose disease is no longer adequately controlled by ruxolitinib alone. Data presented last month at the American Society of Hematology showed that 16 of 26 evaluable patients experienced a reduction in spleen length of at least 50% compared with baseline when treated with the therapy, according to the company.

Company executives said they have held recent discussions with FDA and plan to continue evaluating zavabresib in additional clinical studies as development progresses.