Study to Evaluate Activity of 2 Dose Levels of Imetelstat in Participants With Intermediate-2 or High-Risk Myelofibrosis (MF) Previously Treated With Janus Kinase (JAK) Inhibitor

Overall Response Rate: % of participants with complete remission (CR) or partial remission (PR) per modified IWG-MRT.CR: bone marrow: normocellular <5% blasts, ≤Grade 1 fibrosis; immature myeloid cells in peripheral blood (PB):<2%;hemoglobin (Hb):10 g/dL-upper limit of normal (ULN); neutrophils:1*10^9/L-ULN; platelets: 100*10^9/L-ULN; spleen:not palpable and ≤350ml volume; extramedullary hematopoiesis (EMH): no non-hepato-splenic EMH; symptoms: >70% improvement in symptom score per modified MFSAF v2.0 TSS. PR: bone marrow: normocellular: <5% blasts ≤ Grade 1 fibrosis or not meeting bone marrow remission criteria; Immature myeloid cells in PB: <2%; Hb: 8.5 -<10 g/dL-ULN or 10 g/dL-ULN; neutrophils: 1*10^9/L-ULN; platelets: 50 -<100*10^9/L-ULN; spleen: ≥35% splenic volumetric reduction by MRI or not palpable; EMH: no non-hepato-splenic EMH;symptoms: >50% improvement in symptom score per modified MFSAF v2.0 TSS. All response categories, benefit must last >12 weeks to qualify as response.

CI per the modified 2013 IWG-MRT criteria defined as the achievement of anemia, spleen or symptoms response without progressive disease or increase in severity of anemia, thrombocytopenia, or neutropenia (Increase in severity of anemia constitutes the occurrence of new transfusion dependency or a ≥ 2.0 g/dL decrease in hemoglobin level from pretreatment baseline that lasts for at least 12 weeks. Increase in severity of thrombocytopenia or neutropenia is defined as a 2-grade decline, from pretreatment baseline, in platelet count or ANC, according to the Common Terminology Criteria for Adverse Events (CTCAE) Version 4.03. In addition, assignment to CI requires a minimum platelet count of ≥ 25,000*10^9/L and ANC of ≥ 0.5*10^9/L.) For all response categories, benefit must last for >12 weeks to qualify as a response.

Clinical response rate (CRR) was defined as percentage of participants who achieved CR, PR, or CI per modified 2013 IWG-MRT criteria. CR: bone marrow: normocellular <5% blasts, ≤Grade 1 fibrosis; immature myeloid cells in PB: <2%; Hb: 10 g/dL-ULN; neutrophils: 1*10^9/L-ULN; platelets: 100*10^9/L-ULN; spleen: not palpable and ≤350ml volume; EMH: no non-hepato-splenic EMH; symptoms: >70% improvement in symptom score per modified MFSAF v2.0 TSS. PR: bone marrow: normocellular: <5% blasts ≤ Grade 1 fibrosis or not meeting bone marrow remission criteria; Immature myeloid cells in PB: <2%; Hb: 8.5 -<10 g/dL-ULN or 10 g/dL-ULN; neutrophils: 1*10^9/L-ULN; platelets: 50 -<100*10^9/L-ULN; spleen: ≥35% splenic volumetric reduction by MRI or not palpable; EMH: no non-hepato-splenic EMH; symptoms: >50% improvement in symptom score per modified MFSAF v2.0 TSS. CI: achievement of anemia, spleen or symptoms response without PD or increase in severity of anemia, thrombocytopenia, or neutropenia.

Spleen response per modified 2013 IWG-MRT criteria. Spleen response: a baseline splenomegaly that is palpable at 5-10 cm, below the left costal margin (LCM), becomes not palpable or a baseline splenomegaly that is palpable at >10 cm, below the LCM, decreases by ≥50%; A spleen response requires confirmation by MRI showing >35% spleen volume reduction (SVR). For response categories, benefit must last for >12 weeks to qualify as a response. Participants who achieved CI per modified IWG-MRT criteria considered as response with clinical improvement. Participants who met criteria for spleen response but had worsening cytopenias (and therefore did not meet criteria for clinical improvement) were considered to have a response without clinical improvement. The clinical improvement in IWG-MRT is defined as the achievement of anemia, spleen or symptoms response without progressive disease or increase in severity of anemia, thrombocytopenia, or neutropenia.

Symptoms response per modified 2013 IWG-MRT criteria. Symptoms Response: a ≥50% reduction in the modified MFSAF v2.0 TSS. For response category, benefit must last for >12 weeks to qualify as a response. Participants who achieved CI per modified IWG-MRT criteria considered as response with clinical improvement. Participants who met criteria for symptom response but had worsening cytopenias (and therefore did not meet criteria for clinical improvement) were considered to have a response without clinical improvement. The clinical improvement in IWG-MRT is defined as the achievement of anemia, spleen or symptoms response without progressive disease or increase in severity of anemia, thrombocytopenia, or neutropenia.

Anemia response per modified 2013 IWG-MRT criteria. Anemia response is defined as participants with baseline Hb <10 g/dL but not meeting strict criteria for transfusion dependency: a ≥ 2 g/dL increase in Hb; Transfusion dependent participants at baseline: becoming transfusion independent. Transfusion independence is defined as absence of any pRBC transfusions for at least 12 "rolling" weeks. For response categories, benefit must last for >12 weeks to qualify as a response. Participants who achieved CI per modified IWG-MRT criteria considered as response with clinical improvement. Participants who met criteria for anemia response but had worsening cytopenias (and therefore did not meet criteria for clinical improvement) were considered to have a response without clinical improvement. The clinical improvement in IWG-MRT is defined as the achievement of anemia, spleen or symptoms response without progressive disease or increase in severity of anemia, thrombocytopenia, or neutropenia.

Duration of response (PR/CI/RWCI) is the duration from the date of initial documentation of a response to date of first documented evidence of PD or death, whichever occurs first. PR: BM: normocellular: <5% blasts ≤Grade 1 fibrosis/not meeting BM remission criteria; IMC in PB: <2%; Hb: 8.5 -<10 g/dL-ULN or 10 g/dL- ULN; neutrophils: 1*10^9/L-ULN; platelets: 50 -<100*10^9/L-ULN; spleen: ≥35% splenic volumetric reduction by MRI/not palpable; EMH: no non-hepato-splenic EMH; symptoms: >50% improvement in symptom score. CI: achievement of anemia, spleen or symptoms response without PD or increase in severity of anemia, thrombocytopenia, neutropenia. RWCI: Participants who met criteria for response but had worsening cytopenias. PD: Splenomegaly requires MRI showing ≥25% increase in spleen volume.

Overall Survival is measured from the date of Cycle 1, Day 1 to the date of the participants death. If the participant's was alive or the vital status was unknown, OS was censored at the date that the participant is last known to be alive.

EORTC QLQ-C30 is a questionnaire to assess quality of life of cancer patients. The EORTC QLQ-C30 included 30 items resulting in 5 functional scales (physical functioning, role functioning, emotional functioning, cognitive functioning, and social functioning), 3 symptom scales (fatigue, nausea and vomiting, and pain), and 6 single items (dyspnea, insomnia, appetite loss, constipation, diarrhea, and financial difficulties) which are based on 4-point scale (1= Not at all to 4= Very much); and 1 global health status scale based on 7-point scale (1= Very poor to 7= Excellent). All scales and items are averaged, transformed to 0-100 scale; higher score=better level of functioning. Clinically meaningful improvement defined as change greater than half of the standard deviation at baseline in QLQ-C30 Global Health Status.

EQ-5D-5L is a standardized health-related quality of life questionnaire developed by EuroQol Group in order to provide a simple, generic measure of health for clinical and economic appraisal. EQ-5D-5L consists of two components: a health state profile and VAS. EQ-5D health state profile comprises of 5 dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each dimension has 5 levels: 1=no problems, 2=slight problems, 3=moderate problems, 4=severe problems, and 5=extreme problems. The 5D-5L systems are converted into a single index utility score between 0 to 1, where higher score indicates a better health state. EQ-5D-5L- VAS is designed to rate the participant's current health state on a scale from 0 to 100, where 0 represents the worst imaginable health state and 100 represents the best imaginable health state.

The BPI rates the intensity of pain on 4 items (right now, worst, least, and average), and the interference in 7 areas (general activity, mood, walking ability, normal work, relations, sleep, enjoyment of life). Minimum value = 0; maximum value = 10. Higher scores indicate greater symptom severity/worse outcomes. Clinically meaningful improvement in BPI defined as change greater than half of the standard deviation at baseline.

The PGIC was used to capture the participant's perspective of improvement or decline in MF symptoms over time. The PGIC had a 7-point response scale ranging from 1 to 7 where, (1=very much improved, 2= somewhat improved, 3= a little improved, 4=no change, 5= a little worse, 6= somewhat worse, 7=very much worse).

An AE is any untoward medical occurrence in a participant or clinical investigation participants administered a pharmaceutical product and that does not necessarily have a causal relationship with this treatment. TEAEs were AEs with onset during or after the first dose of study drug, and within 30 days following the last dose of study drug.

Elimination half-life (t 1/2) is associated with the terminal slope (lambda [z]) of the semi logarithmic drug concentration-time curve, calculated as 0.693/lambda(z).