Enasidenib, an Oral Therapy in Mutant IDH2 Relapsed/Refractory Acute Myeloid Leukemia: A Real-Life Single Center Experience
Authors: Riva Marta , Rizzo Lorenzo , Mancini Valentina , Greco Rosa , Bertani Giambattista , Zucchetti Elisa , Diral Elisa , Nichelatti Michele , Veronese Silvio Marco , Grillo Giovanni , Cairoli Roberto 
Published: November 2020

Background:
The treatment for relapsed or refractory acute myeloid leukemia (R/R AML) has minimal chances and a low impact on improving survival. One of the most important goal is to treat unfit patients who are often intolerant to intensive chemotherapy and are not eligible for allogeneic stem cell transplantation. Most patients with AML, including nearly all patients older than 60 years, present multiple, sequentially acquired, somatic mutations. Isocitrate dehydrogenase 2 (IDH2) mutations are present in approximately 8-19% of cases (Buege MJ, Cancers 2018). IDH2 mutations occur early in the leukemogenesis and accumulate an oncogenic product (R-2-hydroxyglutarate) that arrests the histone demethylation pathway, thereby stopping haematopoietic differentiation (Rakheja D, Hum Pathol. 2012).
Enasidenib (ENA) is a selective, powerful oral inhibitor of the oncogenic activity of the IDH2 mutant enzyme, that decreases R-2-hydroxyglutarate levels in vitro and in vivo. Interestingly, phase I/II trials showed an overall response rate (ORR) of 40.3% in R/R disease, with 19.3% of complete remission (CR) and with 6.8 % of CR with incomplete haematological recovery (CRi). Moreover, the reported median overall survival was 9.3 months, with 19.7 months (mo) for patients who achieved CR (Stein E, Blood 2017).
Aims:
To study retrospectively the efficacy and safety of ENA, as single agent, in improving overall survival (OS) and progression-free survival (PFS) in IDH2 mutated R/R AML patients (pts), unfit for intensive chemotherapy. Furthermore, to compare outcomes with a cohort of patients with R/R AML IDH2 wild-type (wt).
Methods:
Since 2018 we have retrospectively collected and analyzed data of unfit IDH2 mutated R/R AML patients, treated with ENA, thanks to the expanded access program of this drug. The dose was 100 mg/day for all pts. PFS and OS were estimated using the Kaplan-Meier product limit method. Therefore, we considered, as historical comparison, a sample of 28 pts with R/R IDH2 wt AML, treated with the best available therapy at our Institution in the same time frame and matched for clinical features. OS and PFS were compared using the log-rank test.
Results:
Nine IDH2 mutated pts were considered for analysis: 4 (44%) cases were de novo AML, while 5 (56%) were secondary (1 myelodysplasia and 4 myeloproliferative neoplasms). Median age at relapse was 71 years (range 47-79). Median number of previous therapies was 2 (range 1-3). All pts completed at least one cycle of ENA with a median number of 5 cycles (range 1-16). Median OS from AML diagnosis and from the beginning of ENA was 28 mo (range 3-65), and 15 mo (range 1-27) respectively; median PFS was 13 mo (range 1-14). Among the 28 patients of the control group, with a median age at relapse of 74 years (range 65-86) we recorded a median OS of 14 mo (range 7-62) and an OS from the last relapse of 2 mo (range 0,5-26). The ENA pts group showed a significantly better OS than the control population (p = 0,0419) (Figure 1). The most prominent toxicities were hyperbilirubinemia in 2 pts (22,2%) and IDH-differentiation syndrome (IDH-DS) in 3 (33,3%); though the drug was generally well tolerated. Therefore, patients were treated as outpatients in most cases.
Conclusions:
In the era of precision medicine, molecular target therapy is the most promising strategy to increase the probability of treatment success with limited side effects. Our experience confirms the efficacy of the IDH2 inhibitor ENA to treat unfit patients with R/R AML in the real life, showing significantly better outcome in terms of survival for the pts treated with target therapy, compared to pts treated with standard therapy.

Disclosures
Veronese: Janssen Cilag:Honoraria;Bayer:Honoraria;Novartis:Other: Travel Expenses;AstraZeneca:Other: Travel Expenses.