Session: 637. Myelodysplastic Syndromes — Clinical and Epidemiological: Poster III
Hematology Disease Topics & Pathways:
Clinical Trials, Workforce, Diseases, Myeloid Malignancies
Results: From 2018-2021, 9 pts were enrolled; all 9 were eligible and evaluable for toxicity and response. Each pt had a detectable Ras mutation at the time of enrollment and was monitored for response using clinical and molecular criteria developed by an international consensus panel (Niemeyer et al, 2015). Five pts were less than 2 years of age. Three patients had relapsed post-HCT prior to enrolling and 6 patients were refractory to a median of 1.5 prior therapies (range 1-3). Four pts had an objective response (1 clinical complete response (cCR), 3 clinical partial responses, (cPR); 2 pts had stable disease and 3 had progressive disease (Table 1). Both pts with stable disease completed the maximum 12 cycles permitted on study. Two pts who achieved a cPR proceeded to HCT. One patient who achieved a cCR remains on study. No molecular responses were achieved. There were no dose-limiting toxicities; one pt had grade 4 thrombocytopenia probably related to trametinib. Of the 8 patients who consented to correlative studies, 7 had DNA methylation testing, 6 had kinome profiling, and 5 had RNASeq testing performed on both pre- and post-trametinib paired samples. DNA methylation testing revealed stable intrapatient methylation signatures across diagnostic, relapse and post-trametinib timepoints using the international consensus criteria (Schönung et al, 2020). Integrated kinome and RNASeq analysis revealed downregulation of proteins and genes involved in Ras/MAPK signaling.
Conclusions: In the first clinical trial for r/r JMML patients in the United States, 4 objective responses were observed among the initial 9 patients meeting the pre-defined criteria to deem trametinib effective. While clinical responses including resolution of splenomegaly, resolution of monocytosis and increased platelets counts were observed, no molecular responses were noted. The treatment of r/r JMML has historically depended on HCT. Recently, azacitidine has shown promise in treating r/r JMML. This trial demonstrates that trametinib is active in r/r JMML and has a favorable side effect profile. Ongoing analysis of extensive correlative testing results have revealed potential mechanisms of response and resistance to MEK inhibition. Future studies will focus on children with newly diagnosed JMML and combine trametinib with azacitidine with or without HCT.
Disclosures: Loh: MediSix therapeutics: Membership on an entity's Board of Directors or advisory committees. Barkauskas: Genentech: Current Employment.
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