This study is testing a drug called Vorinostat to prevent a condition called graft versus host disease (GVHD) in young people receiving a special type of treatment, called allogeneic blood or marrow transplant (BMT). GVHD happens when the new cells from a donor attack the recipient's body. Vorinostat is being added to the usual medicines given to prevent GVHD to see if it works better.

The study will include children, adolescents, and young adults aged 3 to 39 who are undergoing BMT for certain blood cancers or diseases. Participants need to be healthy enough for the transplant, able to take medication by mouth, and agree to follow birth control guidelines to avoid pregnancy during the study.

• The study involves a specific drug regimen, which participants must follow closely.
• Participants will need to have regular check-ups and tests to monitor their health and the effectiveness of the treatment.
• It is important to discuss any past medical issues or current medications with the study team to ensure they are eligible.