Long Term Follow-up and IWG-MRT Response Assessment for 50 Myelofibrosis (MF) Patients Treated with Thalidomide-Prednisone Based Regimens
Authors: Thapaliya Prakash , Tefferi Ayalew , Pardanani Animesh , Steensma David P. , Camoriano John , Wu Wenting , Geyer Susan , Mesa Ruben A. 
Published: October 2019

Abstract
Abstract 4094

Background:
Our group has previously reported the benefits of thalidomide-prednisone based regimens for improvement of anemia, thrombocytopenia, and splenomegaly for patients with MF; both primary myelofibrosis (PMF), and arising from essential thrombocythemia and polycythemia (Post ET/PV MF). We sought to evaluate the overall efficacy of these commonly used regimens by evaluating long-term outcomes and applying the IWG-MRT response criteria (Tefferi et. al. Blood 2006) which arose after completion of these trials.

Methods:
We retrospectively analyzed the long-term outcomes, and assessed the initial therapeutic responses using IWG-MRT criteria from three parallel completed trials of MF using a thalidomide (THAL-50 mg/day) and prednisone (3 month taper beginning at 40mg, stopped at 3 months) backbone. The trials had identical eligibility criteria including adequate organ function and need for MF therapy (defined as symptomatic: anemia and/or splenomegaly). The trials were 1) THAL-PRED alone, THAL only after 3 months 2) THAL-PRED-etanercept (ETAN - TNF- alpha inhibitor at 25 micrograms subcutaneously twice a week), THAL and ETAN only after 3 months and 3) THAL-PRED – oral cyclophosphamide (CTX 25mg daily orally), THAL alone after 3 months.

Results:
Patients: A total of 50 pts were enrolled in these 3 trials (Males n=36, 72%) with median age of 68.5 years (Range 43–85), with 79% having PMF. Patients had advanced disease in general with 88% having intermediate 2 or high risk MF by IWG criteria (Cervantes et. al. Blood 2009), 62% patients with red cell transfusion dependence and 50% with an abnormal karyotype.

Therapy initial results:
80 % of patients reached the three month juncture on the trials, with 40% reaching 6 months. Initial toxicity was myelosuppression with 3 cases of grade 3 anemia, 3 cases of grade 3 neutropenia and 4 cases of grade 3 thrombocytopenia. There were no grade 4 or higher hematological toxicities noted. Initial neuropathy was uncommon and seen in only 4% of patients. No complete responses were observed and only 1 patient had partial response (by IWG-MRT criteria). 14 patients (28% overall) met the new IWG-MRT criteria for clinical improvement; 11 for anemia (22%), 2 for thrombocytopenia (4%) and 3 for splenomegaly (6%). Responses occurred relatively quickly at an overall median of 8 weeks (range 4–12) after enrollment.

Long Term Outcomes:
After a median follow-up of 36 months across this cohort we observed an overall median duration of response of 8.5 months (range 3–42). Responses to THAL based regimens can lead to periods of prolonged stabilization after cessation of therapy. We observed an overall median time to institution of next therapy of 3 months (range 1–50). At the time of this analysis 14 patients (28%) have expired of their MF and median survival across the entire cohort was 36 months (3-106).

Comparison of Regimens:
Comparison of these three independent trials (Table 1) suggests greater toxicity and inferior response rate, duration of response, and time to next therapy with the cyclophosphamide containing regimen.

Conclusion:
THAL-PRED based regimens are active in a subset of MF patients for therapy primarily of anemia, and for some patients a response of good duration (even after cessation of therapy) may be obtained. IWG-MRT response assessment demonstrates utilizing additional agents to a THAL-PRED regimen do not appear to augment (and may detract from responses). Newer agents such as pomalidomide may have similar to greater efficacy without neuropathy and less myelosuppression.

Disclosures:
Off Label Use: There is no FDA approved agent in Myelofibrosis. All the drugs discussed; Thalidomide, Prednisone, Etanarcept and Cyclophosphamide are off-label. Mesa:SBio: Research Funding; Novartis: Research Funding; Celgene: Research Funding; Incyte: Research Funding; Roche: Research Funding; eisai: Research Funding; telik: Research Funding.