Rigel to present R289 data in lower-risk MDS and new fostamatinib results in ITP at ASH 2026 – Rigel

Rigel Pharmaceuticals will present updated Phase 1b data for R289 at the 68th ASH Annual Meeting, in an oral session on 12 December 2026. R289 is the company’s investigational dual IRAK1/4 inhibitor, and the data cover patients with relapsed or refractory lower-risk myelodysplastic syndrome (MDS).

R289 in lower-risk MDS

As of 16 July 2026, 64 patients had enrolled: 33 in the dose-escalation phase and 31 in the dose-expansion phase. Most were elderly and heavily pretreated, and most had a high transfusion burden at baseline. R289 continues to be generally well tolerated. The oral presentation will include the first efficacy data from the randomised dose-expansion phase, including the effect on transfusion dependence.

R289 is a prodrug of R835. It blocks toll-like receptor and IL-1 receptor signalling, which is thought to drive the chronic bone marrow inflammation behind persistent low blood counts in lower-risk MDS.

“We continue to be encouraged by our evolving data in this heavily pretreated patient population,” said Alison L. Hannah, MD, Rigel’s chief medical officer.

Fostamatinib in ITP and wAIHA

• Combination therapy in ITP. A real-world analysis looked at 90 patients who received fostamatinib plus a thrombopoietin receptor agonist (TPO-RA). Of the 38 patients with platelet measurements in months 7 to 12, 81.6% had platelet counts of at least 50 × 10³/µL. At baseline, 33.3% of all 90 patients had counts at that level.
• Japanese post-marketing surveillance. An interim analysis of 799 patients found no new safety signals. Platelet counts rose within two weeks of starting treatment, and responses were maintained at 12 months in a subset of patients with follow-up data.
• Long-term extension in wAIHA. Among 71 patients, more than half had durable haemoglobin responses through week 104. Safety was consistent with fostamatinib’s known profile. Fostamatinib remains investigational in wAIHA.

The R289 data will be presented orally, alongside three posters on fostamatinib in immune thrombocytopenia (ITP) and warm autoimmune haemolytic anaemia (wAIHA).