Bomedemstat vs Hydroxyurea for Essential Thrombocythemia (MK-3543-007)

The purpose of this study is to evaluate the efficacy and safety of bomedemstat compared with hydroxyurea in cytoreductive therapy naïve essential thrombocythemia (ET) participants for whom cytoreductive therapy is indicated. Its primary objective is to compare bomedemstat to hydroxyurea with respect to durable clinicohematologic response (DCHR). The primary hypothesis is that bomedemstat is superior to hydroxyurea with respect to DCHR.

Inclusion Criteria: * Diagnosis of Essential Thrombocythemia (ET) based on World Health Organization Criteria for myeloproliferative neoplasms, and an indication for cytoreductive therapy regardless of age or risk status * Has a centrally assessed bone marrow fibrosis score of Grade 0 or Grade 1, as per a modified version of the European Consensus Criteria for Grading Myelofibrosis * Has received no prior cytoreductive treatment for their ET * Human Immunodeficiency Virus (HIV)-infected participants have well controlled HIV on antiretroviral therapy * Participants who are Hepatitis B surface antigen (HBsAg) positive are eligible if they have received Hepatitis B Virus (HBV) antiviral therapy for at least 4 weeks and have undetectable HBV viral load * Participants with history of Hepatitis C Virus (HCV) infection are eligible if HCV viral load is undetectable Exclusion Criteria: * History of any illness/impairment of gastrointestinal function that might interfere with drug absorption * History of a malignancy, unless potentially curative treatment has been completed with no evidence of malignancy for 2 years * HIV-infected participants with a history of Kaposi's sarcoma and/or Multicentric Castleman's Disease * Has an active infection requiring systemic therapy * Has had a major surgery \<4 weeks prior to first dose of study intervention or has not recovered from side effects of major surgery \>4 weeks prior to first dose