A Phase 3, Randomized, Double-blind, Active-Comparator-Controlled Clinical Study to Evaluate the Efficacy and Safety of Bomedemstat (MK-3543) Versus Hydroxyurea in Cytoreductive Therapy Naïve Essential Thrombocythemia Participants

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