Long-term use of fostamatinib was effective in patients with immune thrombocytopenia (ITP) and rheumatoid arthritis (RA), and no new safety concerns were observed, according to study results presented at the British Society for Haematology 2021 Virtual Annual Meeting.

Fostamatinib is an oral spleen tyrosine kinase (SYK) inhibitor that couples immune cell receptors to intracellular signaling pathways. Fostamatinib has been effective in treating patients with ITP. For this study, safety data on fostamatinib in patients with ITP were pooled from 2 randomized, double-blind, placebo-controlled, phase 3 studies and 1 long-term, open-label extension study. A total of 13 phase 2 and phase 3 studies of fostamatinib treatment in patients with RA were included as well.

A total of 146 patients with ITP and 3437 patients with RA were included in the study’s analysis. In terms of patient characteristics, 60% of patients with ITP and 83% of patients with RA were women; the median ages were 53 years and 54 years, respectively; and the mean durations of treatment with fostamatinib were 19 months and 18 months, respectively.

Continue Reading

The most common adverse events (AEs) seen with fostamatinib treatment included diarrhea (36% of patients with ITP; 24% of patients with RA), hypertension (22% of patients with ITP; 19% of patients with RA), and nausea (19% of patients with ITP; 8% of patients with RA).

In addition to these common AEs, some disease-related AEs were associated with ITP but not with RA. These included epistaxis (19% ITP; 0.5% RA), petechiae (15% ITP; 0.3% RA), contusion (12% ITP; 2% RA), and fatigue (10% ITP; 2% RA). Worsening of RA was seen in 9% of patients in the RA group only.

Further, there were 58 patients who received fostamatinib treatment for more than a year, for whom over time the researchers observed a decrease in the frequency of AEs, a decrease in the use of rescue therapy, and an increase in median platelet counts.

“The safety profile…has been consistent and manageable. No new safety concerns were observed with chronic dosing compared to short-term dosing. Long-term dosing studies provided no evidence of cumulative toxicity with long-term treatment,” the researchers concluded in their presentation.

Disclosure: This clinical trial was supported by Rigel Pharmaceuticals. Please see the original reference for a full list of authors’ disclosures.


Hill Q, Tong S, Numerof R, Stacey D, Datangel J, Masuda E. Long-term safety of fostamatinib, an oral spleen tyrosine kinase inhibitor, in treating immune thrombocytopenia and rheumatoid arthritis. Poster presented at: British Society for Haematology 2021 Virtual Annual Meeting; April 25-28, 2021; virtual.