Status Change

Merck closes enrollment in Phase 3 bomedemstat trial for essential thrombocythemia

The 300-patient study versus hydroxyurea moves to Active, not recruiting on schedule, keeping Merck's second pivotal bomedemstat trial in essential thrombocythemia on track for its 2027 readout.

The Phase 3 MK-3543-007 trial of bomedemstat against hydroxyurea in essential thrombocythemia moved from Recruiting to Active, not recruiting, with its 300-patient target reached and its primary completion date holding at September 28, 2027.

By AppliedXLJuly 17, 2026Trial NCT06456346

Executive Summary

Merck's Phase 3 trial testing bomedemstat against hydroxyurea in newly diagnosed essential thrombocythemia closed enrollment at its target size and moved to active follow-up, a routine transition that keeps the study on its stated timeline.
This is one of two pivotal bomedemstat trials in essential thrombocythemia, and the first in patients who have never received cytoreductive treatment, making it the study most likely to define bomedemstat's front-line positioning.
The completion date has held steady since its last revision, and the enrollment count matched target exactly, both consistent with a trial tracking to its guided schedule rather than showing distress.
Bomedemstat is the most advanced LSD1 inhibitor in essential thrombocythemia, with no other program in the class having reached Phase 3 in this indication, positioning this readout as the one that will show whether LSD1 inhibition can beat a decades-old chemotherapy standard.

The transition

NCT06456346, known as MK-3543-007, shifted from Recruiting to Active, not recruiting on July 17, 2026, according to the trial's registry record. The change followed the trial reaching its enrollment target of 300 patients across sites in the United States, Japan, France, Spain, Turkey, Israel, the United Kingdom, Germany, and China. The trial tests bomedemstat, an oral LSD1 inhibitor, against hydroxyurea in patients with essential thrombocythemia who have not previously received cytoreductive therapy, with a primary endpoint of durable clinicohematologic response, a composite measure of platelet control, absence of white-cell elevation, and freedom from thrombotic events or disease progression through week 52. NCT06456346

Probability of Success

Endpoint Met65%

Completes82%

Clinical Significance55%

Regulatory71%

Why the setup matters

Bomedemstat is running two separate Phase 3 programs in essential thrombocythemia: this trial in treatment-naive, first-line patients, and a second study in patients with an inadequate response or intolerance to hydroxyurea. Both are designed around the same durable-response endpoint. The first-line design in this trial tests whether an LSD1 inhibitor can displace hydroxyurea as initial cytoreductive therapy, a broader claim than a second-line study of patients who have already failed the standard drug.

Timing and stability

The trial's primary completion date has moved twice since the study began: first pulled forward from May 2029 to April 2027 in November 2024, then pushed back to September 28, 2027 in October 2025. It has held at that date for roughly nine months since the last revision, and the enrollment figure closing exactly at its 300-patient target represents no change against the operational model's routine threshold for enrollment swings. Eligibility criteria were amended twice, adding a centrally assessed bone marrow fibrosis grading requirement, a refinement of population definition rather than a shift in what the trial tests. NCT06456346

The competitive field

LSD1 inhibition in essential thrombocythemia is a field with few active entrants: five trials study the target in this indication, and none has been terminated to date. Bomedemstat is the only LSD1 inhibitor to reach Phase 3 here; the nearest peers, Jubilant Therapeutics' JBI-802 and Incyte's INCB059872, remain in Phase 1 or Phase 2 testing across broader myeloproliferative neoplasm populations. Hydroxyurea itself, the comparator arm, remains the established first-line cytoreductive agent in this setting, so this trial's bar is not whether bomedemstat shows activity, but whether it can separate from the decades-old standard on durable response without added thrombotic or hemorrhagic risk. NCT06456346

This analysis was produced using AI-assisted reporting systems, AppliedXL data, and official public records. These systems undergo editorial review, quality checks, and regular audits by human experts. Errors may still occur, as with any automated system. Always consult the linked primary sources. Read our AI Editorial Policy.