Long term outcomes of ET and PV patients after clinical trial treatment with interferon alfa

Abstract Background Polycythemia vera (PV) and essential thrombocythemia (ET) are chronic myeloproliferative neoplasms (MPN) characterized by myeloproliferation and an increased risk of thrombohemorrhagic complications, progression to myelofibrosis (MF), and reduced overall survival. Risk-adapted management of PV/ET favors treatment with cytoreductive therapy in high-risk patients. Hydroxyurea (HU) is the most frequently utilized first-line cytoreductive agent, however pegylated interferon alpha-2a (PEG) and the more recently approved, ropeginterferon alfa-2b (ropeg-IFN), have demonstrated a potential to induce molecular responses and improve event free survival (EFS) (Gisslinger Leukemia 2023). The Myeloproliferative Neoplasms Research Consortium (MPN-RC) 111 and 112 investigator-initiated clinical trials established the efficacy and safety of PEG in both treatment naïve (n=82) and HU intolerant/resistant (n=115) patients. MPN-RC 111/112 reported results up to 36 months with a median duration of treatment of about 24 months (Yacoub Blood 2019, Mascarenhas Blood 2022). This study aims to characterize the longer-term follow-up and outcomes of 111/112 trial patients treated at our center after the study terminated. Methods This is a single center retrospective review of 34 patients with high-risk ET or PV who were treated on the 111/112 trials with PEG and continued to be followed at Mount Sinai. IRB approval was obtained prior to data capture. Therapies initiated after PEG were examined, including duration of treatment, therapy-free intervals, and response to subsequent therapies. Clinical outcomes (during/after trial enrollment) included thrombotic/hemorrhagic events, progression to MF, leukemic transformation, hematopoietic stem cell transplantation (HSCT), and death. PEG related toxicity data included development of hypothyroidism, autoimmune disease, depression/mood disorder, liver dysfunction, and ocular toxicity. Results 34 patients were included in the analysis (16 ET and 18 PV) with median age of 73.5 years. 26 (14 PV and 12 ET) were enrolled on 111 from 2012 to 2015 and 8 (4 PV and 4 ET) were enrolled on 112 from 2011 to 2016. 26 (81.3%) patients had mutations in JAK2, 3 (9.4%) in CALR, 1 (3.1%) in MPL, and 2 (6.3%) were triple-negative. At 12 months on trial, 12 (35.3%) patients achieved a complete response, 12 (35.3%) had a partial response, and 10 (29.4%) had no response to PEG. The median duration of follow up was 104.8 months after trial termination. 8 patients received no further therapy after the end of study, 12 received one subsequent therapy, and 14 received two or more subsequent therapies. 13 patients continued receiving commercial PEG or received it at some interval after study end and 2 patients were treated with ropeg-IFN. The median duration of PEG was 25.3 months on trial and 30.9 months when including those who continued on commercial PEG after trial termination. Median EFS was 140.4 months (95% CI 121.1 - Not estimated) including 5 (15%) patients with a thrombotic event, 1 (3%) with a hemorrhagic event, 8 (24%) progression to MF, 1 (3%) HSCT, 1 (3%) leukemic transformation, and 5 (15%) who died (2 second primary malignancies, 1 sepsis, 1 hemorrhage, 1 unknown). 25 of 34 patients developed toxicities potentially related to PEG therapy, including hypothyroidism (n=3), autoimmune disease (n=4), depression/mood disorder (n=10), liver dysfunction (n=13) and ocular toxicity (n=2). DiscussionPEG therapy is an effective therapy for ET and PV with the potential for durable responses. With a median follow up of more than 8 years, this single center retrospective analysis demonstrated a long EFS of greater than 11 years, accompanied by low rates of leukemic transformation and MPN-related death. There was no statistical difference in EFS based on response to PEG at 12 months on the initial 111/112 trials. The relatively short duration of PEG therapy may explain the rates of MPN-related events, including thrombosis and progression to MF. Future analyses should identify additional predictors of EFS, including duration of PEG treatment, best response to PEG at certain landmark intervals, and depth and/or duration of molecular response. This analysis also demonstrated high rates of PEG-related toxicities, although definitive causality was often difficult to determine. Additional clinical and molecular data will be available at the time of the meeting.