Successful Discontinuation of Eltrombopag Treatment in Patients with Chronic ITP
Authors: Leven Emily , Miller Allison , Boulad Nayla , Haider Anis , Bussel James B 
Published: October 2019

Abstract
Abstract 1085

Introduction:
Patients with immune thrombocytopenia (ITP) commonly experience platelet increases while under treatment with thrombopoietin-receptor agonists (TPO-RA). Anecdotal evidence suggests certain patients have been able to discontinue TPO-RA and still maintain platelet counts above baseline without additional treatment. This prospective ongoing study was designed to investigate the frequency and characteristics of patients exhibiting sustained responses after electively discontinuing eltrombopag (a TPO-RA) without substituting additional therapy.

Methods:
Enrolled patients were required to have ITP defined by consensus guidelines (Provan, Blood, 2009) for at least 6 months and must have been taking eltrombopag for a minimum of 4 months prior to starting this observational study. Rescue therapy is permitted once in the first 4 weeks off eltrombopag. The primary response endpoint was prospectively defined as a platelet count of ≥30,000/μl and ≥20,000/μl above initial baseline for 6 months off eltrombopag without intervening treatment (other than rescue). The secondary endpoint was being stably off therapy at 4 weeks after discontinuing eltrombopag. All patients who meet the 2 inclusion criteria (ITP for 6 months and eltrombopag for 4 months) are eligible for the study.

Results:
Fifteen patients are currently enrolled. Ages range from 3 to 86 years, median 55 years, with 10 females. There are 5 responders of 5 months or more (3 females, 2 males) and 10 non-responders (7 females, 3 males). Four of 5 responders have been off therapy for 6 months or more; the fifth “responder” has been off therapy for 5 months, with platelet counts ≥195,000/μL (figure 1). Responders are aged 19–86 years and have had ITP for 5–34 years; all had been on eltrombopag for > 2 years. Two responders were splenectomized and all had 3 or more prior therapies. One responder and 9 non-responders received rescue treatment in the first 4 weeks. One patient was a responder at 4 weeks, but she lost her response before reaching 6 months off-treatment. Factors not significantly associated with response were: age, duration of ITP, duration of eltrombopag therapy, splenectomy status, number of prior ITP treatments, bleeding history, and platelet count at the time that eltrombopag was discontinued. However, a lower absolute immature platelet fraction (AIPF) value at cessation of eltrombopag was seen in responders (fig 2, p=0.022). AIPF data for 1 non-responder is not available. An AIPF of 900 × 10/μl at the time of discontinuation of eltrombopag exceeds the AIPF of all 5 responders, but also of 3 of 9 non-responders.

Conclusions:
A substantial fraction of patients with ITP treated with eltrombopag, approximately 1/3, appear able to discontinue eltrombopag treatment and nonetheless maintain an at least adequate platelet count indefinitely (at the very least 6 months). Similar preliminary data has been reported with romiplostim (EHA and ASH abstracts).
AIPF values (platelet retics) may better predict a patient's likelihood of successfully stopping therapy than other variables such as those listed above.

Disclosures:
Bussel: Amgen: Family owns Amgen stock Other, Membership on an entity's Board of Directors or advisory committees, Research Funding; Cangene: Research Funding; GlaxoSmithKline: Family owns GSK stock, Family owns GSK stock Other, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genzyme: Research Funding; IgG of America: Research Funding; Immunomedics: Research Funding; Ligand: Membership on an entity's Board of Directors or advisory committees, Research Funding; Eisai: Membership on an entity's Board of Directors or advisory committees, Research Funding; Shionogi: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sysmex: Research Funding; Portola: Consultancy. Off Label Use: The use of romiplostim in pediatric patients was examined in this study.