A Study to Evaluate Safety and Efficacy of Bomedemstat (MK-3543-017)

Inclusion Criteria: * Is from a bomedemstat study sponsored by Imago BioSciences, Inc. (a subsidiary of Merck \& Co., Inc.) or MSD, and established by the Sponsor as MK-3543-017 ready * Has received at least 6 months of treatment with bomedemstat in the IMG-7289-202/MK-3543-005 study, while safely tolerating bomedemstat, and receiving clinical benefit from its use in the estimation of the investigator * ET and PV participants from established feeder studies other than IMG-7289- 202/MK-3543-005 must have achieved confirmed hematologic remission, must be safely tolerating bomedemstat, and must be receiving clinical benefit from its use in the estimation of the investigator * Is not currently on a dose hold * Participant must be able to swallow oral medication and follow instructions for at-home dosing of bomedemstat Exclusion Criteria: * Has received prohibited concomitant medications * Ongoing or planned participation in another investigational study * Has noncompliance in prior bomedemstat study receiving \<90% of assigned doses excluding suspensions or holds as assigned by the investigator