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Rigel Presents Updated Data from Ongoing Phase 1b Study at ASH Annual Meeting

Rigel Pharmaceuticals, Inc. (RIGL) | December 7, 2025

By Ian Walker

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Rigel Pharmaceuticals presented updated data on R289 in patients with lower-risk MDS at the 67th ASH Annual Meeting.

Preliminary efficacy was observed in elderly lower-risk MDS patients at doses of ≥500 mg QD.

R289 was generally well tolerated, with 33% achieving RBC-TI at doses ≥500 mg QD.

Difficult-to-Treat Population

33 patients enrolled, median age 75, heavily pre-treated lower-risk MDS patients.

Safety Profile

R289 well tolerated with common Grade 1/2 TEAEs including diarrhea, constipation, fatigue.

Efficacy Highlights

6/18 transfusion dependent patients achieved RBC-TI with >8 weeks duration at doses ≥500 mg QD.

  • The data highlights the potential of R289 as a treatment option for transfusion dependent lower-risk MDS patients.
  • Steady state R835 plasma concentrations at doses ≥500 mg QD reached levels associated with significant inhibition of cytokine release.

The updated data on R289 demonstrates promising preliminary efficacy and safety in the difficult-to-treat lower-risk MDS patient population. The findings suggest R289's potential as a valuable treatment option for these patients.