The 'Stop TPO-RA in ITP Patients' study: Clinical and immune modulatory effects of romiplostim tapering

Sustained remissions off-treatment (SROTs) after tapering of thrombopoietin receptor agonists (TPO-RAs) have been reported in 15%-50% of patients with immune thrombocytopenia (ITP). The STIP (Stop TPO-Receptor Agonist in ITP Patients) study is a prospective trial aimed to investigate the clinical effects of romiplostim tapering. Adult patients (22/40) with ITP ≥3 months received romiplostim for 1 year, were tapered and followed for 1 year. Anti-platelet antibodies (APAs), TPO levels and indium-111 platelet scintigraphy were assessed before, during and after romiplostim. Censored survival analysis showed that the probability of SROT at 1 year after tapering was 23.6% (95% confidence interval: 11.0%-50.5%). Patients with SROT had higher platelet levels on romiplostim (median: 332.5 vs. 84.5 × 10⁹/L) and lower romiplostim doses at the start of tapering (median: 1.0 vs. 4.5 μg/kg) compared to those with a non-sustained response (NSR). APAs were detected in 8/25 patients at baseline, of which 5 showed a substantial decrease during romiplostim. The indium-111 scan revealed an improved platelet survival at the start of tapering for 50% of patients with SROT (2/4, missing n = 1) versus none with an NSR (0/14, missing n = 3). Overall, the STIP study demonstrated a probability of SROT of 23.6% in a diverse and largely chronic group of adult patients with ITP.