Background: Omacetaxine mepesuccinate (“omacetaxine”) is a first-in-class, reversible, transient inhibitor of protein elongation that facilitates tumor cell death without depending on BCR-ABL signaling. Clinical activity was shown in two phase 2, open-label, multicenter studies in treatment-resistant CML. Methods: A subset from the phase 2 studies included patients in CP or AP who were resistant/intolerant to ≥2 approved TKIs. Omacetaxine 1.25 mg/m² was given SC twice daily: ≤14 consecutive days/28-day cycle for induction, ≤7 days/cycle as maintenance. Secondary results were calculated for responses by number of prior TKIs. Results: Of 122 patients (median age, 60 years), 62 had received 2 TKIs (100% imatinib; 76% dasatinib; 24% nilotinib) and 60 had received all 3 approved TKIs. Prior non-TKI therapies (eg, 52% hydroxyurea, 34% interferon) were common. Of 45 CP patients in the 2 TKI group, 12 (27%) had major cytogenetic response (MCyR; median duration of 17.7 mo), and of 36 in the 3 TKI group, 4 (11%) had MCyR (median duration not reached). Of 17 AP patients in the 2 TKI group, 6 (35%) had major hematologic response (MaHR; median duration, 13.4 mo), and of 24 in the 3 TKI group, 5 (21%) had MaHR (median duration, 6.4 mo). Median months of survival in the 2 and 3 TKI groups were 30.1 and not reached for CP and 12.0 and 24.6 for AP. Treatment-related grade 3/4 adverse events (AEs) occurred in 52 (84%) patients in the 2 TKI group and 42 (70%) in the 3 TKI group (most common: thrombocytopenia [71%, 48%]). Fifteen (24%) and 16 (27%) had an AE leading to discontinuation, primarily disease progression. There were 20 deaths (primarily disease progression), 11 in the 2 TKI group and 9 in the 3 TKI group; 4 were considered related to treatment (sepsis in 2, pancytopenia, febrile neutropenia). Conclusions: In patients with heavily pretreated CML, response to omacetaxine therapy occurred whether they had received 2 or 3 prior TKIs. The drug was well tolerated. Tolerability was similar across the TKI groups in both CP and AP patients. Support: Teva Pharmaceutical Industries Ltd.