A Study of Bomedemstat (IMG-7289/MK-3543) Compared to Best Available Therapy (BAT) in Participants With Essential Thrombocythemia and an Inadequate Response or Intolerance of Hydroxyurea (MK-3543-006)

DCHR rate is the percentage of participants with DCHR, defined as a confirmed reduction of platelet count to ≤400 × 10^9/L and absence of white blood cell (WBC) count elevation to >10 × 10^9/L locally assessed to be due to ET, starting by Week 24 and maintained for at least 24 weeks, and the absence of any thrombotic or major hemorrhagic events or disease progression to myelofibrosis (MF), myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) by Week 52.

CHR rate is the percentage of participants with CHR, defined as a confirmed reduction of platelet count to ≤400 × 10^9/L and absence of WBC count elevation to >10 × 10^9/L locally assessed to be due to ET, maintained for at least 12 weeks, and the absence of any thrombotic or major hemorrhagic events or disease progression to MF, MDS or AML by Week 52.

HR rate is the percentage of participants with HR, HR is defined as the time from the first confirmed hematologic response to first documented evidence of confirmed platelet increase or confirmed WBC increase after latest confirmed hematologic response date.

The PROMIS Fatigue SF-7a is a 7-item participant-reported assessment that measures both the experience of fatigue and the interference of fatigue on daily activities over the past week. Response options are on a 5-point Likert scale, ranging from 1 = never to 5 = always. The total score is used in the analysis and is obtained by summing keyed scores of all items. Scores can range from 7 to 35, with higher scores indicating greater fatigue.

The MFSAF v4.0 is a 7-item participant-reported myelofibrosis symptom assessment which asks respondents to report symptom severity at its worst for each of the 7 items on a 0 (Absent) to 10 (Worst Imaginable) numeric rating scale.

For participants who demonstrate DCHR, DODCHR is defined as the time from the first documented evidence of confirmed reduction of platelet and WBC counts until confirmed increase of platelet and WBC counts to above acceptable threshold, thrombotic or major hemorrhagic events, or disease progression to MF, MDS or AML.

For participants who demonstrate CHR, DOCHR is defined as the time from the first documented evidence of confirmed reduction of platelet and WBC counts until confirmed increase of platelet and WBC count to above acceptable threshold, thrombotic or major hemorrhagic events, or disease progression to MF, MDS or AML.

For participants who demonstrate HR, DOHR is defined as the time from the first confirmed hematologic response to first documented evidence of confirmed platelet increase or confirmed WBC increase after latest confirmed hematologic response date.

Thrombotic events include but are not limited to new or recurrent acute myocardial infarction, unstable angina, stroke, transient ischemic attack, deep venous thrombosis, pulmonary embolism, thrombotic digital ischemia, or other thrombotic events.

Major hemorrhagic events include but are not limited to fatal bleeding, and/or symptomatic bleeding in a critical area or organ such as intracranial, intraspinal, intraocular, retroperitoneal, intra-articular or pericardial, or intramuscular with compartment syndrome, and/or bleeding causing a decrease in hemoglobin level of 2 g/dL or more, or leading to transfusion of 2 or more units of whole blood or red cells.

Disease progression rate is the percentage of participants with disease progression, defined as the transformation to post-ET MF, MDS, or AML as assessed by the adjudication committee.

An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention.

An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention.