Fostamatinib may become a treatment option for warm antibody autoimmune hemolytic anemia (AIHA), a different form of cold agglutinin disease, according to a phase 2 multicenter open-label study recently published in the American Journal of Hematology.

Patients with warm AIHA usually have scarce treatment options when primary treatment fails. Fostamatinib is an oral tyrosine kinase inhibitor approved in the United States to treat other autoimmune conditions, such as chronic immune thrombocytopenia.

In this phase 2 study, the authors evaluated fostamatinib administration (150 mg twice a day) in patients with warm AIHA who had active hemolysis with a hemoglobin level <10 g/dL and did not improve with at least 1 prior treatment. For patients experiencing adverse events, their doses were adjusted to 100 mg twice a day, 150 mg 4 times a day, 100 mg 4 times a day, or the drug was discontinued.

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The study’s primary endpoint was hemoglobin level >10 g/dL with an increase in hemoglobin ≥2 g/dL from baseline by week 24 without requiring rescue therapy with red blood cell transfusion. Eleven of 24 (46%) patients reached the primary endpoint, with an increase in median hemoglobin level detected at week 2 that was steadily sustained. The median lactate dehydrogenase level and reticulocyte count declined over time with small changes in the median haptoglobin level.

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“Fostamatinib increased [hemoglobin] levels in previously treated patients with [warm AIHA], with clinically meaningful [hemoglobin] responses observed in nearly half of patients,” the authors said. “The [hemoglobin] response was rapid and durable. Responders most often were female, had secondary AIHA and had fewer prior AIHA medications than non-responders.”

The most common adverse events were diarrhea and fatigue in 42% of patients, followed by hypertension, dizziness, and insomnia in 27%, 27%, and 23% of patients, respectively. These were expected according to the safety database and manageable, and the authors reported no new safety signals. Other second-line therapies like rituximab are used for patients with warm AIHA, although their efficacy remains unclear due to the heterogeneity of study designs and contrasting results.

“Limitations of this study are the small sample size, lack of a control or comparator arm, lack of [direct antiglobulin test] results after treatment, and a relatively short duration of follow-up,” the authors concluded.

“Potential comparisons to other studies treating patients with [warm AIHA] should be interpreted with caution due to differences in study design, definitions of response, and patient characteristics, particularly the type and number of prior treatments.”


Kuter DJ, Rogers KA, Boxer MA, et al. Fostamatinib for the treatment of warm antibody autoimmune hemolytic anemia: phase 2, multicenter, open‐label studyAm J Hematol. Published online February 18, 2022. doi:10.1002/ajh.26508