South San Francisco, California, United States, November 4, 2026
Rigel Pharmaceuticals, Inc. has announced that updated clinical data from its ongoing Phase 1b study of R289, an investigational dual interleukin receptor-associated kinase 1 and 4 (IRAK1/4) inhibitor, will be presented in an oral session at the 68th American Society of Hematology (ASH) Annual Meeting and Exposition. The study is evaluating R289 in patients with relapsed or refractory (R/R) lower-risk myelodysplastic syndrome (MDS) who have not responded adequately to previous treatments. The upcoming presentation will include updated findings from both the dose-escalation and randomized dose-expansion phases, with particular attention to safety, clinical activity and potential reductions in transfusion dependence. As of July 16, 2026, 64 patients had been enrolled in the study. The announcement represents an important milestone in Rigel’s hematology research program and highlights continued efforts to develop new treatment options for patients with difficult-to-treat bone marrow disorders.
R289 Phase 1b Study Advances in Lower-Risk MDS
The ongoing Phase 1b clinical study is investigating R289 in adults with relapsed or refractory lower-risk MDS. The condition is a group of bone marrow disorders in which blood-forming cells develop abnormally, often resulting in insufficient production of healthy red blood cells, white blood cells and platelets. Patients may experience anemia, infections, bleeding complications and an increased need for blood transfusions. The study includes two development stages: dose escalation and dose expansion. According to Rigel, the trial had enrolled 33 patients in the dose-escalation phase and 31 patients in the dose-expansion phase as of July 16, 2026. The majority of participants were considered to have a high transfusion burden at baseline, reflecting the significant disease-related challenges faced by this heavily pretreated population. R289 is an oral prodrug of R835, a potent and selective inhibitor of IRAK1 and IRAK4, two enzymes involved in inflammatory signaling pathways. These kinases participate in biological processes that can influence immune-cell activity, inflammation and abnormal cellular behavior. By inhibiting both targets, R289 is being investigated for its potential to modify disease-associated signaling pathways in MDS. The company previously presented dose-escalation findings at the 2025 ASH Annual Meeting. The 2026 presentation will provide an updated assessment that also incorporates findings from the randomized dose-expansion stage.
Updated Clinical Data to Highlight Safety and Transfusion Outcomes
According to Rigel, R289 has continued to demonstrate a generally well-tolerated safety profile in the elderly and heavily pretreated lower-risk MDS population evaluated so far. The company indicated that updated information from a planned mid-November 2026 data cutoff will be included in the upcoming oral presentation. A major focus will be the potential effect of treatment on red blood cell transfusion dependence. Many patients with lower-risk MDS develop persistent anemia and require repeated transfusions to maintain adequate hemoglobin levels. Reducing or eliminating this requirement can be an important treatment objective because transfusion dependence affects patients’ quality of life and may contribute to iron overload and other complications. The randomized dose-expansion phase is expected to provide additional information about the efficacy and safety of R289 at the selected dose levels. However, the November data analysis has not yet been completed, and detailed updated efficacy results have not been disclosed in the November 4 announcement. The oral presentation is scheduled for December 12, 2026, from 3:00 p.m. to 3:15 p.m. Central Time, during the ASH Annual Meeting in New Orleans, Louisiana. Hematology specialist Guillermo Garcia-Manero, MD, will present the findings.
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Rigel Highlights Additional Hematology Research at ASH
In addition to R289, Rigel will present three scientific posters featuring data for TAVALISSE® (fostamatinib disodium hexahydrate) in immune-mediated blood disorders. One presentation will examine real-world outcomes associated with combining fostamatinib and thrombopoietin receptor agonists (TPO-RAs) in patients with immune thrombocytopenia (ITP). Among 38 patients with available platelet measurements during months seven to twelve, 81.6% achieved platelet counts of at least 50,000 per microliter, compared with 33.3% of the 90 patients at baseline. A second presentation will report interim findings from a Japanese post-marketing surveillance study involving 799 patients with ITP. The analysis found no new safety signals, while platelet counts increased within two weeks of treatment initiation. A third presentation will examine long-term hemoglobin responses in 71 patients with warm autoimmune hemolytic anemia (wAIHA) enrolled in an extension study. More than 50% demonstrated durable hemoglobin responses during follow-up through Week 104. Fostamatinib remains investigational for wAIHA. Overall, Rigel’s participation at ASH 2026 highlights its continued focus on hematologic diseases and emerging treatment approaches. The upcoming R289 presentation will be particularly important for understanding the candidate’s clinical development potential in lower-risk MDS. Further patient follow-up and larger clinical studies will be needed to establish its long-term efficacy and safety.
Source: Rigel Pharmaceuticals press release
