This study is testing a new medicine to help people with a certain illness.
If you join, you'll be randomly picked (like flipping a coin) to get either the real medicine or a fake one (called a placebo). Everyone will also get another medicine called enzalutamide.

• You'll take pills every day - some with food, some without.
• Doctors will check your health often with things like blood tests, heart checks, and pictures of your body.
• You'll visit the clinic every 4 weeks for about a year, then less often after that.
• Even if your illness gets worse, you might still keep taking the medicine if it's helping you.
• This study is not the usual way doctors treat this illness, but it might help in the future.

Metastatic Castration-Sensitive Prostate Cancer

Adults with a certain kind of prostate cancer that has spread.
They must be healthy enough to join and follow the rules of the study.

They can join if they:

• Have prostate cancer confirmed by doctors
• Have cancer that has spread to bones or other parts of the body
• Have not taken certain cancer medicines before
• Can safely take the study medicine
• Can swallow pills
• Are not recovering from major surgery

They cannot join if they:

• Have serious heart, brain, or stomach problems
• Have had other types of cancer (with some exceptions)
• Have taken certain medicines or treatments recently
• Have had thoughts of hurting themselves in the past year
• Are using medicines that aren’t allowed in the study

This study is testing a new medicine called mevrometostat.
Doctors want to see if it works better when used with another medicine called enzalutamide.
They are studying adults with a kind of prostate cancer that has spread but still responds to certain treatments.
The goal is to find the safest and best dose of the new medicine and see how it affects the body.