Pomalidomide in Myelofibrosis with Cytopenia: First Results of the Mpnsg 01–09 Study (ClinicalTrials.gov Identifier: NCT00949364).
Authors: Schlenk Richard F , Reiter Andreas , Gattermann Norbert , Hebart Holger , Jost Edgar , Platzbecker Uwe , Hochhaus Andreas , Waller Cornelius F. , Schafhausen Philippe , Blau Igor W. , Verbeek Walter , Werner Martin , Kreipe Hans H. , Mahler Carolin , Mack Silja , Schauer Stefanie , Ostlender Sabine , Stegelmann Frank , Benner Axel , Griesshammer Martin , Döhner Konstanze 
Published: October 2019

Abstract
Abstract 2840

Background:
Pomalidomide in a single arm phase-I/II study and one randomized four arm phase-II study in primary myelofibrosis (MF) and post-polycythemia vera/essential thrombocythemia (post-PV/ET) MF showed efficacy in particular with respect to improvement in anemia. To date, pomalidomide has been evaluated in MF at two dose levels, 0.5mg and 2.0 mg/day.

Aims:
To evaluate clinical efficacy of pomalidomide alone and in combination with prednisolone (PRED) in patients with primary or post-PV/ET MF and cytopenia.

Methods:
The main inclusion criteria for primary or post-PV/ET MF patients were red blood cell (RBC)-transfusion-dependence or hemoglobin <10 g/dl, and/or thrombocytopenia <50/nl and/or neutropenia <1.0/nl; patients >=50 years were eligible. Treatment consisted of pomalidomide (POM) 2mg/day; prednisone (PRED) 30mg/day was added in patients who did not respond (≤ stable disease) within three months of therapy. The primary endpoint was response assessed by IWG criteria and extended by the criterion red blood cell transfusion-independence (Gale RP et al., Leuk Res. 2011). Concurrent hydroxyurea in patients with proliferative disease and aspirin 100 mg/d in patients with platelets between 50/nl and 1000/nl were administered. The statistical design of the study was based on the Simon optimal two-stage design. Here we report on the first stage of the study. Median follow-up according to the method of Korn was 18 months.

Results:
Thirty-eight patients were treated with POM 2 mg/d, the median age was 71 years (range 51–83), 34% were female. Twenty-seven had primary and 11 post-PV/ET MF. Disease stage at study-entry according to the DIPSS was high-risk in 13 (34%), intermediate-2 risk in 22 (58%) and intermediate-1 risk in 3 (8%). Incidence of high-risk cytogenetics, JAK2 V617F mutation and MPL W515L mutation were 29% (10/34), 55% (21/38) and 18% (7/38), respectively. Twenty-seven patients (71%) were RBC-transfusion- and 7 (18%) platelet-transfusion dependent. Median duration of treatment with POM was 11.4 months with 5 patients continue on treatment 24+ months. PRED was added after 3 months in 19 of 28 eligible patients. POM dose-reduction (n=8, 1mg/d; n=2, 0.5mg/d) was performed after a median time of 34 days (range 3–308 days) due to fatigue (n=2), thrombo- and/or neutropenia (n=7), rash (n=1). Seven patients with high risk characteristics (n=6 RBC-transfusion dependent, n=4 high risk cytogenetics) experienced transformation into blast phase (BP), the actuarial probability of transformation to BP measured from diagnosis was 6.0% (SE 4.1%) at 2 years and 22.4% (SE 8.4%) at 5 years. Response was observed in 14 patients (37%) after a median time of 4.8 months (n=1 complete remission, n=5 clinical improvement-platelets, n=3 clinical improvement-erythrocytes, n=5 red cell transfusion-independence); 8 responders received concomitant PRED and responded after a median of three months (range 0.8–11.7 months) of the addition of PRED. In 5 of 14 responders POM dose was reduced due to toxicity, notably before response occurred. Responses were observed within the first 3 months (n=4), between month 4 to 6 (n=4) and beyond month 6 (n=6) with the latest response seen at 12.7 months. There was no correlation between response and JAK2/MPL mutation status or cytogenetics. Basophilia defined as greater than 50% increase in absolute basophil count at month 3 was in trend associated with response (p=0.06).

Conclusions:
POM with or without PRED in patients with different risk groups of patients with primary and post-PV/ ET MF was effective with a response rate of 37%. Based on results of this first cohort the protocol was amended; i) POM dose has been adjusted to 0.5 mg/d, ii) up-front randomization of PRED at month 4 or month 7 in patients without response but stable disease to single agent POM was introduced.

Disclosures:
Schlenk: Celgene: Research Funding. Off Label Use: Pomalidomide is so far not approved for the treatment of primary and secondary myelofibrosis.