This study is testing the safety and effects of a new drug called INCB057643 on people with myelofibrosis (MF) and other blood diseases. Myelofibrosis is a condition where scar tissue forms in the bone marrow, affecting blood cell production. The study is for adults 18 and older who have tried other treatments without success.

• The study has two parts: one tests INCB057643 alone, and the other tests it with a drug called ruxolitinib.
• Participants must have tried at least one other therapy and not have better treatment options.
• The study involves regular visits and monitoring, but it does not mention any payment for participation.

Participants must agree not to get pregnant or father a child during and shortly after the study. You cannot join if you’ve used a similar type of drug or have certain health issues like active infections or uncontrolled conditions. Some medical tests and doctor approval are needed to join. Always talk to your doctor to see if joining a study is the right choice for you.