Trial Drug: Anagrelide

This is a study evaluating the safety and efficacy of bomedemstat (MK-3543) compared with the best available treatment (BAT) in participants with essential thrombocythemia (ET) who have an inadequate response to or are intolerant of hydroxyurea.

The primary study hypothesis is that bomedemstat is superior to the best available treatment with respect to durable clinicohematologic response (DCHR).