Mirum Pharmaceuticals, Inc. (MIRM) and Incyte (INCY) announced positive pivotal Phase 2 results from Cohort 1 of the PROGRESS study evaluating the investigational asset Zilurgisertib in adolescents and adults aged 12 years or older with Fibrodysplasia Ossificans Progressiva (FOP). Results were presented at the Endocrine Society's annual meeting, ENDO 2026.
FOP is an ultra-rare genetic disease in which skeletal muscle and connective tissue, such as tendons and ligaments, are gradually replaced by bone.(Source-NIH).Mirum estimates that it affects approximately 300 patients in the U.S. and 900 worldwide, with diagnosis typically occurring in early childhood.
Zilurgisertib
Zilurgisertib is an investigational oral small-molecule inhibitor of activin receptor-like kinase 2 (ALK2/ACVR1). In FOP, mutant ALK2 signalling is abnormally activated, driving heterotopic ossification (HO)—the formation of bone in muscles, tendons, ligaments, and other soft tissues.
Mirum obtained exclusive worldwide rights from Incyte in 2026. Notably, Zilurgisertib is awaiting the FDA decision on its NDA for FOP in September 2026.
Trial Details
PROGRESS is a global, randomized, double-blind, placebo-controlled Phase 2 study evaluating the efficacy and safety of zilurgisertib in patients with Fibrodysplasia Ossificans Progressiva.
Cohort 1 enrolled patients aged 12 years and older who were randomised 1:1 to receive zilurgisertib 100 mg once daily or placebo during a 24-week double-blind treatment period, followed by an open-label extension.
The proportion of cohort 1 patients with new heterotopic ossification (HO) lesions on whole-body CT at week 24 is the primary endpoint. Key secondary endpoints include the number and total volume of new HO lesions, changes in total HO lesion volume and flare activity through week 24.
Key Findings
-In patients treated with Zilurgisertib, fewer patients developed new HO Lesions at week 24 with an 81% reduction versus placebo.
-99.9% reduction in total volume of new HO lesions in patients receiving zilurgisertib versus placebo at Week 24.
-Among patients receiving Zilurgisertib, no new HO lesions were observed, and total HO lesion volume continued to decrease from week 24 to week 48, said Mirum.
-No new lesions were observed, and the total HO lesion volume decreased from week 24 to week 48 in patients who crossed over to placebo.
-According to the firm, the data showed that Zilurgisertib was generally well tolerated during the 24-week placebo-controlled period of the study.
MRIM has traded between $47.89 and $114.99 over the last year. The stock closed Friday's (12-06-2026) trade at $99.35, down 0.20%.
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