RESULTS of Allogeneic TRANSPLANTATION for Polycythemia VERA and Essential Thrombocythemia
Authors: Ballen Karen K , Arora Mukta , Zhu Xiaochun , Agovi Manza , Kalaycio Matt , Maziarz Richard T , Cortes Jorge E. , Woolfrey Ann , Horowitz Mary M. , Saber Wael 
Published: October 2019

Abstract
Abstract 3514
Polycythemia vera (PV) and Essential Thrombocythemia (ET) are myeloproliferative neoplasms (MPN). Although most affected persons have prolonged survival, survival is compromised in patients with unresponsiveness to therapy, transformation to blastic phase, and progression to myelofibrosis. Allogeneic transplantation may be considered an option in selected patients, but there have been no large scale studies to date. We analyzed the outcomes of 77 ET patients and 44 PV patients who had undergone allogeneic transplantation between 1990 and 2007 and were reported to the CIBMTR (n= 96) or Fred Hutchinson Cancer Center (n=25). Patients who had transformed to acute myelogeneous leukemia were excluded from this analysis. Median age of subjects with ET was 48 years (range 20–64) versus 53 years (range 30–66) for patients with PV. Thirty-two patients received an HLA identical sibling transplant (MRD), 64 a matched unrelated donor transplant (MUD), and 23 a partially matched unrelated donor transplant (MMUD). Median time from diagnosis to transplant was 92 (4-1000) and 120 (5-326) months respectively. Median follow-up of survivors was 51 months (11-169) for ET and 52 months (3-154) for PV. Karnofsky performance status was &gt; 90% in 56% of ET patients and 57% of PV patients. The majority of patients (69% for ET and 64% for PV) received an ablative conditioning regimen. About 25% of patients received radiation in the conditioning regimen. The incidence of neutrophil and platelet engraftment at 28 days was 87% and 57% for ET patients and 86% and 62% for PV patients. Acute GVHD Grades II-IV and III-IV was 57% and 27% for ET patients and 50% and 28% for PV patients. Incidence of chronic GVHD at 5 years was 47% for ET and 49% for PV. Transplant related mortality (TRM) at one year was 26% for ET and 23% for PV. There was recurrent disease at 5 years in 14% of ET and 31% of PV patients. Overall survival (OS) at 3 and 5 years was 59% and 56% respectively for ET and 70% and 65% respectively for PV. Progression free survival (PFS) at 3 and 5 years was 50% and 47% respectively for ET and 46% and 46% respectively for PV. The unrelated donor patients had a lower percentage of neutrophil engraftment at Day 28: 100% for MRD, 90% for MUD, and 95% for MMUD (p &lt;0.001). Platelet engraftment, acute GVHD, relapse, OS, and PFS were similar among the different graft sources. The most common causes of death were GVHD, organ failure, and infection. Twenty-six patients (22%) had transformed to myelofibrosis at the time of transplant. There was no significant difference in TRM, OS, or PFS between patients with and without transformation to myelofibrosis. Forty-seven patients (39%) had splenomegaly at the time of transplant and 33 patients (27%) had a prior splenectomy. Neutrophil and platelet engraftment at day 28 were superior in the patients with normal spleen size or splenectomized patients (p = 0.005 and 0.006 respectively) compared to patients with splenomegaly, but there was no difference in GVHD, TRM, OS, or PFS. In conclusion, 1) Over 45% of patients transplanted for ET and PV are long term progression free survivors; 2) Transformation to myelofibrosis did not significantly impact TRM, OS, or PFS; 3) Patients with normal spleen size or post splenectomy had improved neutrophil and platelet engraftment compared to patients with splenomegaly, but no impact on TRM, OS, and PFS; 4) Patients receiving unrelated transplants had similar OS and PFS to MRD; 5) Allogeneic transplantation is a potentially curative therapy for selected patients with ET and PV. The role of allogeneic transplantation in the treatment of these disorders needs to be defined in comparison to emerging non-transplant based treatments.

Disclosures:
No relevant conflicts of interest to declare.