Long-term sustained response to fostamatinib in two patients with chronic refractory immune thrombocytopenia (ITP)

Real-world clinical outcomes with fostamatinib for the treatment of refractory chronic immune thrombocytopenia: a single-center experience

Fostamatinib is a spleen tyrosine kinase inhibitor indicated for the treatment of chronic immune thrombocytopenia (ITP) unresponsive to a previous treatment. Real-world studies evaluating the utilization and effectiveness of fostamatinib outside the context of a clinical trial are lacking. The objective of this analysis was to evaluate the effectiveness of fostamatinib for the treatment of ITP in a real-world cohort. We conducted a single-center, retrospective, observational study to evaluate the effectiveness of fostamatinib for the treatment of ITP. The primary endpoint was durable response as defined by the American Society of Hematology ITP response criteria. Secondary endpoints included overall response rate, time to response, and safety. Subgroup analysis was performed to assess frequency of durable response in key subgroups of patients based on prior therapies. Thirty-one patients treated with fostamatinib for ITP were included in our analysis. Patients had received a median of four prior lines of therapy. Ten patients (32%) achieved a durable response. Most durable responders maintained their response at 24 months ( n  = 7; 70%). The median time to response was 9 days. Four patients (13%) discontinued fostamatinib due to an adverse event. Subgroups who had higher rates of durable responses included those who had received two to three prior lines of therapy (40%), splenectomized patients (50%), and those who had not received prior rituximab (55%). Fostamatinib therapy in a real-world population of patients with heavily pretreated ITP led to a durable response in a third of patients, which was maintained for most responders.

Eltrombopag plus cyclosporine in refractory immune thrombocytopenia: a single-center study

Background

With the development of thrombopoietin receptor agonists, the prognosis of immune thrombocytopenia (ITP) in patients in whom there was a poor response to first-line treatment has greatly improved. However, there are still some patients who are refractory to eltrombopag.

Objectives

To explore the efficacy and safety of eltrombopag combined with low-dose cyclosporine in the management of patients with refractory ITP.

Methods

A total of 21 participants with ITP who failed to respond to multiple lines of therapy (including a daily dose of 75 mg of eltrombopag for at least 30 days) treated at The First Affiliated Hospital of Zhejiang Chinese Medical University between January 2018 and August 2022 were included. All enrolled patients subsequently received 50 mg of eltrombopag daily and low-dose cyclosporine (3 mg/kg/d, with an initial target concentration of 75-120 ng/mL). The efficacy and safety of the combined therapies were evaluated.

Results

A total of 76.2% (16/21) of the patients responded to the combination of cyclosporine and eltrombopag, with a median time to response of 14.5 (range, 5-37) days. A complete response (platelet count ≥ 100 × 10⁹/L) was observed in 81.3% (13/16) of the patients, among whom 1 patient experienced relapse due to self-reduction in eltrombopag. During a median follow-up of 180 days, there were no relapses, and 70% (7/10) of the patients successfully stopped or decreased concomitant ITP medications. One patient had both a catheter-related deep vein thrombosis and a venous cerebral thrombotic event later; no other severe drug-related adverse events were observed.

Conclusion

Combining low-dose cyclosporine with eltrombopag may be an effective alternative for multirefractory ITP that is nonresponsive to eltrombopag alone.

Recent progress in ITP treatment

In this review, the recently approved drugs avatrombopag and fostamatinib, which were not extensively covered within 2019 international recommendations for ITP, will be discussed in some detail. Avatrombopag appears more convenient than eltrombopag as it does not require dietary restrictions or subcutaneous administration like romiplostim. However, data on quality of life (QoL) are lacking and the rate of thromboembolic events in exposed patients is not negligible. Efficacy of fostamatinib, an inhibitor of macrophagic activity, is supported by placebo-controlled trials in patients refractory to several therapies, including TPO-RA. While hypertension and diarrhea have been reported, only one minor thrombotic event occurred in 146 exposed patients. In addition, several new treatment combinations and new agents entered clinical investigation in recent years. In a UK trial, combining mycophenolate mofetil with corticosteroids as first line therapy was more effective than corticosteroids alone, but at the cost of worse QoL. No combination, including oseltamivir or all-trans retinoic acid or danazol, resulted in convincing evidence of superior efficacy and safety when used in first or later lines of treatment. Agents targeting specific mechanisms are also discussed: sutimlimab (complement inhibitor); rilzabrutinib (BTK inhibitor) and efgartigimod (modified Fc fragment inhibiting FcRn). Only efgartigimod has completed phase 3 investigation.

Emerging Therapies in Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is a rare autoimmune disorder caused by peripheral platelet destruction and inappropriate bone marrow production. The management of ITP is based on the utilization of steroids, intravenous immunoglobulins, rituximab, thrombopoietin receptor agonists (TPO-RAs), immunosuppressants and splenectomy. Recent advances in the understanding of its pathogenesis have opened new fields of therapeutic interventions. The phagocytosis of platelets by splenic macrophages could be inhibited by spleen tyrosine kinase (Syk) or Bruton tyrosine kinase (BTK) inhibitors. The clearance of antiplatelet antibodies could be accelerated by blocking the neonatal Fc receptor (FcRn), while new strategies targeting B cells and/or plasma cells could improve the reduction of pathogenic autoantibodies. The inhibition of the classical complement pathway that participates in platelet destruction also represents a new target. Platelet desialylation has emerged as a new mechanism of platelet destruction in ITP, and the inhibition of neuraminidase could dampen this phenomenon. T cells that support the autoimmune B cell response also represent an interesting target. Beyond the inhibition of the autoimmune response, new TPO-RAs that stimulate platelet production have been developed. The upcoming challenges will be the determination of predictive factors of response to treatments at a patient scale to optimize their management.