Platelet Kinetic Study (PKS) May Early Identify a Subset of Patients with Immune Thrombocytopenia (ITP) Probably Cured by Romiplostim. Two Years Follow-up

(TPO)-receptor agonists (romiplostim and eltrombopag) are new therapeutic modalities in the treatment of ITP. Romiplostim treatment was associated with a number of benefits compared with the standard of care in non splenectomized ITP patients: higher platelet response rate, lower rates of treatment failure and splenectomy, fewer bleeding events, and fewer blood transfusions. Nevertheless there are not enough data on the long-term side effects and economic consequences of prolonged treatment. Furthermore, there are no criteria to identify patients potentially cured and that could stop therapy. For all these reasons we have carried out a study of platelet kinetics in all patients treated with TPO- receptor agonists and we have identified a subset who achieved a normal platelet kinetics and that is no longer relapsed two years after discontinuation of the drug

A total of 18 adult patients, female (63%),median (range) age 55 (31 – 78) years, median (range) baseline platelet count 19 (3 – 32) × 109/L.,median of 4 (1 – 7) prior ITP therapies, received romiplostim administered once weekly sc, with dose adjustments to maintain platelet counts in the target range of 50–150×109/L. The median time since ITP diagnosis was 6,8 years (range, 0.6–12.8 years) and 10% had undergone a splenectomy. Patients received romiplostim for a median of 98 weeks (range, 18–104); taking the average weekly dose of all patients, the median was 4 mcg/kg. Home administration was started by 16% of patients (3/18) but 2/3 patients discontinued home administration and resumed weekly outpatient injection. All patients achieved a platelet count ≥50×109/L.

3 out of 18 experienced thrombocytosis and rebound thrombocytopenia. A PKS with (111)In oxine-labeled autologous platelets was performed in all patients failing steroid treatment, before romiplostim was started. A gamma function was used for the calculation of platelet mean life span (MLS) that was greatly reduced in 100% of patients.3 patients, who had achieved early a stable platelet count ≥150×109/L. despite the discontinuation of romiplostim maintain normal platelet count after 24 months of follow-up. Stricking a second PKS six months after starting the treatment showed in these subset, a normal platelet half-life with normal uptake on the spleen and liver.

In our opinion PKS, in romiplostim responding patients who discontinued treatment for the stability of response, may easily detect patients probably cured

No relevant conflicts of interest to declare.