Inclusion Criteria:

• Diagnosis of essential thrombocythemia according to revised World Health Organization (WHO) 2016 criteria.
• Resistant to or intolerant of hydroxyurea, that is, fulfilling at least 1 of the following criteria:
  • Platelet count > 600 × 10^9/L after 3 months of at least 2 g/day of hydroxyurea (2.5 g/day in subjects with a body weight over 80 kg) OR at the subject's maximally tolerated dose if that dose is < 2 g/day.
  • Platelet count > 400 × 10^9/L and WBC count < 2.5 × 10^9/L or hemoglobin < 10 g/dL at any dose of hydroxyurea.
  • Presence of leg ulcers or other unacceptable mucocutaneous manifestations at any dose of hydroxyurea.
  • Hydroxyurea-related fever.
• Platelet count > 650 × 10^9/L at screening.
• WBC > 11.0 × 10^9/L at screening.

Exclusion Criteria:

• Subjects previously treated with anagrelide or JAK inhibitors.
• Inadequate liver function at screening and Day 1 (before drug administration) as demonstrated by:
  • Total bilirubin > 1.5 × upper limit of normal (ULN)
  • Aspartate aminotransferase or alanine aminotransferase > 1.5 × ULN
  • Hepatocellular disease (eg, cirrhosis)
• Inadequate renal function at screening as demonstrated by creatinine clearance < 40 mL/min calculated by Cockcroft-Gault equation.